The lighter the better for off roading, a typical military sized trailer really has no need for 2x4 120 box tubing. Way over built. 2X2 would be more than adequate. Draw it up, or as close as you can get to it. Lay it out on the floor and look at at it. If you are putting a fridge in it, put it where you plan for it to go, fuel, batteries, same thing actually set things around so you see the size you want and need. Take your time and find what works for you if you are building it. Have fun is the main thing in building one.