THE PLAN – Trailer

2011 Interstate Cargo – Full Conversion

Getting into a DIY trailer build can be a very rewarding experience. But it can also be full of pitfalls and expenses you never dreamed of. You need to have a total plan from the very start. I enjoyed my build for sure. I have even built my own house, doing all phases of the construction. So I have knowledge and skill sets many do not have. I also have an arsenal of specialty tools.

If self satisfaction is not your primary motivator I suggest you think real hard. I thought I could save money. I thought I could build a better mousetrap.

In hindsight I do not believe I saved any money. My trailer foot by foot compared to a commercially built trailer of comparable size is way heavier. This means you also better be thinking of your Tow Vehicle capabilities before jumping into the project.

The normal person does not have access to many of the lighter RV materials, appliances, devices, or wiring components. Especially not at wholesale and with the buying power the big boys have. Many construction aspects of my trailer makes it a true RV type trailer. With many of the bells and whistles. It is not a bare bones camping convenience one step up from a tent. It is not a tear drop. For aerodynamic reasons, in hindsight I wished I had purchased a V-nose trailer. My one ton chevy van which gets close to 20 MPG on the highway normally, gets 8-9 MPG towing my trailer. Add some head wind to that and I have seen worse.

I know now I could have purchased a used commercially built RV trailer and have been out less money and had been camping in the time frame I was converting my trailer. Even needing to replace or repair items on a used trailer would have been a whole lot less time and money. But the satisfaction factor was a motivator with me. At times I think I need to reevaluate that in the future.

I also doubt the resale value of my trailer has appeal to the larger audience of buyers out there that would prefer a name brand and the availability of financing.

I have also found insurance issues and the fact RV Roadside Insurance carriers such as Good Sam’s will not cover a DYI trailer that holds a Utility classification still on the Title.

The FRAME (DIY Concerns)

If you are still ready to dive in you need a plan.

For some that might mean evaluating an existing trailer frame sitting in your garage, your skills to perhaps construct one from scratch, or purchasing a frame to build on.

For my latest project I personally purchased a brand new tandem axle cargo trailer. One with a high enough ceiling to meet my objectives.

Many people on their first build tackle the project without any clue of where they are going. Perhaps some hand drawings on scraps of paper? Dreams? Or that other extreme. The engineering type that lays out numerous CAD drawings? Both these extremes often forget about the very basic of basics. That frame! The frame, axle, bearings, suspension, wheels, and tires. They buy a very inadequate base to start with. Or something that can never work.

Many first builds are teardrop type trailers. Built on old frames from boat trailers or newer Harbor Freight type lightweight trailers. There are many groups on social media you can explore. I caution that you don’t believe everything you read or see. Many are so proud of their creation that they fail to point out things that are wrong with the build. Many trailer frames used would not pass a legal “weigh in” for gross/net, etc. It may never come up unless you cause an accident. Then you might find yourself in nasty litigation for negligence. Some states may require you to get a legal weigh in to license the trailer.

My first major item of concern is focused on the frame, and any DIY/Homebuilt. The laws concerning trailers, registration, licensing, and insuring, differ wildly from State to State. In some States you could build your trailer and never be able to take it on the road. I can’t stress this enough. Research this prior to wire brushing your first piece of rust, or cutting your first piece of wood. Think into the future as well. Just because you can license your trailer in your state, that might not hold true in another (think resale). You might even get involved in illegally running your trailer in another state?

I have been around and have bought and sold trailers through the years. The most sickening feeling is to purchase a used trailer (lets use an old one as an example). The seller gives you a bill of sale. Never had a title or registration because he/she never needed one. You spend time and money building your project. Try to license it and you can’t. This happens to many people. Especially when dealing with used, and across state lines.

Don’t believe anything a seller or another person tells you. Ultimately it is up to you to know. Find out from your state DMV. Be honest with your questioning. I personally would not start out unless the trailer has a VIN number, Bill of Sale, and a Title in which the VIN matches on all. And then you have had it licensed and already road legal.

Even then you need to inquire whether you will be able to create a Home-built and License it in your state. It may be wise to license it first before starting your construction? But does that make it illegal after the fact once it is an RV Trailer licensed as a Utility Trailer? What happens to a trailer that the title states utility trailer and you are going to use it a an RV/Camp/Live in it, Even then some states are weird and this becomes an illegally licensed trailer if the title and registration aren’t updated. Some states may make you jump through hoops, to get you to the stage of attaching a license plate.

Once you get all your ducks in a row before investing in your frame, find out about insuring it. Or getting Insurance for Roadside assistance. I had a recent axle problem that required flat bedding my trailer to get it home. I was only 19 miles from my drive. The tow company bill was over $300.

With some tow vehicle policies you have some coverage as long as you are hooked to the tow vehicle. Great for collision and such. Detached and sitting at a campsite or in your drive that type of arrangement could leave you with a destroyed or stolen trailer. With no recourse for reimbursement. Attempting to insure the trailer alone, as an RV gets real sketchy. It will differ wildly from Company to Company. Might I highly suggest you get it in writing so it is very clear this is a home built and what is stated on the title are covered the way you might “assume” it is.

My cargo conversion still carries the Utility classification on the title. I contacted Good Sam’s to add there RV trailer roadside assistance coverage. They would not cover it since the title was as a Utility. I was very clear up front. I didn’t want the situation where when I went to use it they would not cover me and point out some obscure clause in their contract. Apparently there is just that. I called several times just to make sure I was getting the same story. They would not cover mine.


Electrical components are the second major concern. We are not going to touch on the electrical and wiring for the basic trailer operation such as brake lights, running lights, and turn signals. Though these are integral parts, we are going to assume everything is installed and working properly associated with those.

We are talking 12VDC Cabin Lighting, running a water pump, 110VAC Power outlets, 110VAC to 12VDC Converter-Charger, Portable Device Charging Options, Inverters and Solar, the ability to connect to Shore/Park power, etc.

In the very basic of systems you normally find a Auxiliary Battery. In the basic system everything in the trailer is 12VDC powered. You charge the battery up at home and hope the battery does not discharge into the damage zone while you are out camping.

Starting to add to that basic configuration people start connecting the Trailer Auxiliary Battery to their tow vehicles charging system This allows you to charger your trailer battery while traveling down the road. With this configuration everything is still 12VDC

While hardcore basic camping type people are quite satisfied with being totally 12VDC many others are not. I call it one step above tent camping.

In your “Plan” you need to think long and hard. Many try to add some form of 110VAC after the fact. Planning for it ahead of your build will save you money and make a much neater and safer installation.

Let me touch on this for the DIYer. You will find some RV Parks will not allow you in, or will not allow you to connect to the power unless your trailer has a RVIA sticker (Recreation Vehicle Industry Association). Which I find almost laughable after working on some of the wiring and plumbing in commercial rigs sporting the sticker. Just know that is out there. I have run into it once in a National Park RV site campground, and at one very “uppity” RV Park. I try to avoid the “uppity” RV Parks anyway. Then ironically I have camped at the same National Park RV site campground on other occasions and was never confronted. There always has to be the overly anal person/camp host you encounter once in a blue moon.

That said, I would definitely seek the help of a licensed electrician to help you with the 110VAC end of things. You need to make sure you properly protect your rig, your person, and 110VAC electrical sources you plug into. There is much to know about properly grounding, adhering to proper polarity of connections, Fuses/Breakers, and load/wire gauge considerations.

After you progress beyond just using 12VDC, things start getting more complicated. Many want to install a device called a Converter-Charger. Specially a Converter for changing Shore/Park Power (110VAC), to 12VDC to power your 12VDC circuits, as well as charging and maintaining the Trailers Auxiliary Battery. Those camping at campgrounds with power pedestals , and for more than a day or two, usually end up installing these Converter – Chargers. A couple of brands come to mind. The Progressive Dynamics Model PD4045, or the WFCO Model WF8730. These are both ideal units for handling your 110VAC and 12VDC. Providing a main 110VAC breaker, Branch 110VAC Breakers, and Fused Distribution for all of you 12VDC circuits. Be sure to ground this unit to your incoming 110VAC power connection, metal trailer frame, and metal skin. The National Electrical Code concerning RV’s requires this power to chassis ground/bond, be a minimum #8 copper, and includes ground bonding any metal exterior skin.

Other Sources of charging or power is to also add in Solar, Generators, and Inverters.


This is another area that may require professional assistance. Plan ahead.

Things to consider are inside runs verses outside runs if you camp in freezing weather.

Fresh water storage tanks need located to balance weight over the axle. While Black and Gray tanks are not so critical if you always dump when leaving a campground.

RV Water pumps are 12VDC and have a reverse flow check valve built into them. Running a “T” after the pump to also have a “City” pressurized water connection requires a check valve in the “City” side of your system too.

All sinks, showers, etc plumbed to the gray waste holding tank need traps installed in the drain, and these vented to the outside above the roof line, to avoid gases and fumes entering the living compartment through the drain lines.

The black tank needs vented to outside the living compartment above the roof line. Any commode that dumps into the black waster storage tank needs to be an RV type the seals off after flushed to also avoid fume entering the living area.

Most try to tie the gray and black vents together inside walls or partitions, then run a single vent pipe out of the ceiling/roof. There is a special exterior cover made for that configuration.

I like to use PEX for the hot and cold water supply lines. I prefer the brass connectors and elbows over the plastic ones many commercial trailer manufactures are using. The plastic ones seem to crack too easily. Regular home grade fixtures, verses RV type, have given me better long term service without problems.