Thinking about a Rig

Thinking about what kind of rig we might want to start the journey with. It's not going to be easy to make the transition from being house bound to RV bound. We don't want to have a lot of money invested in a rig before the house is sold, otherwise, we could be making payments on both. But if the house sells before our January retirement date then we'll need something to live in until, at least until then. Our 1999 F150 with tow package is rated for 8,000 lbs. I think we could look for a trailer between 6-7,000 lbs empty...if we are to use it. In that range we aren't looking at anything very long, or with slides, probably something less than 30' in the light or ultralight category. Those can be had, used, in the $10-$15k range. When we have a little more experience on the road we could purchase something larger. But how hard is it to sell a trailer in that range? Are they worth anything on a trade-in? How do you do it all without a permanent address?