Placing a travel trailer on our recreational property?

Regs and getting it set up are the 2 biggest hurdles, IMO. I'd see how you can get by with it legally if you intend on leaving it there.
Second, yes I'd build a roof over it if your talking 10-20 years. No question.
It will save you the time money and pain in the @ss with leaks.

Realistically this is one of those questions that none of us can answer any of the specifics on unless we have experience in the same area. (Other than theoretical stuff like it rains, put a roof over it).