I have been randomly thinking about my camper build a lot over the last few months but have not been able to start it just yet. So I will throw out some ideas that I have been considering. The frame itself well be constructed out of 2x2" steel tubing and 2" C channel. I think this will be the easiest and reasonably light without losing some strength. The tongue will be constructed of tube channel for the center with C channel for the angles coming down. I wanted to keep it the standard 50 degree angle incase I want to fit a standard tongue box up front. All the cross members will be constructed of C channel as well. This should allow me to drill through them to allow for wiring to pass through for any electrical needs like lights and breaks.
Another item I would like to mount under the camper would be a ProPex HS2211 propane furnace. I would probably mount this in the last open section under the camper and then make one large skid plate for the water tank and the heater. This unit is designed for the exterior of a vehicle, so it should do just fine under the camper. This would require gas to be plumbed from a 20lb tank mounted on the tongue to the back. this would be needed for a cook stove and for a shower anyways.
I will also be using the axle-less system from Timbren Axles. Above are some with the brake kit installed. Since this will be an off-road/overlanding style camper, these made the most sense when it come to the design of the camper frame itself. They still require a 2x2" cross member that will add strength to the axles and also a mounting point for the skid plate.
So far these are the ideas that I feel pretty solid about. I am always open for suggestions on what works and what won't work, but would really try to utilize the above mentioned items for the frame build and try to plan around other items if needed. I know I will probably have to build out my own custom fenders and such. Also the use of angle iron under to act as a wire or gas line tray is probably something that would allow me to both secure and protect those items under the trailer.