A lot depends on how many people will be in it, if you are full time living in it, want to stand up, want a full bathroom, how much solar panel space you need, how long you want to stay and where on BLM land you want to go. We have basically done everything from a tent, VW bus, Honda Civic, 6’ truck topper, 80” camper trailer, 7’ truck camper, 11’ camper trailer, 21’ motor home, 24’ toy hauler, 25’ camper trailer and a 28’ motor home not in that order and had no real problems as most government thinking was areas should be designed for camping rigs less than 28’. Only place we have ever seen anything smaller was National Bridges National Park and camped on BLM land near by. After watching 35’ fifth wheels go down 4x4 only roads at Lake Powell I don’t think any thing is impossible it just depends on how much you can afford to fix! There will always be places on BLM land you can’t get to but there is always some where you can. In general the smaller the rig the more options for locations you will have.