7x14 is going to be a tandem axle so by the time it is built out it will be too heavy. Cargo trailers are usually not allowed in RV parks. If you tow anything at that vehicles max weight it's going to be a pita. I'd also think that a small toy hauler is your answer after upgrading to stout 1/2 ton or a 3/4 ton truck. A lot of 16 ft TH also have wet bath so moving up to 20 ft or so would probably put you in dry bath models. I know you are planning on holding tanks but if you do use some other toilet system be aware that SOME blm areas require holding tanks or you are required to park within X distance of the outhouses.
As a rule of thumb I would suggest shooting for using about 1/2 of a tow vehicles capability and maybe end up at 60 % or so. Do you have option code 53 G?
