Pick which state you want to setup domicile check the options for mail forwarding service.
Check on registration, DL's,insurance.
Much easier to have this decided on before hand.
We don't boondock very often so have not gone the solar panel way. We did camp off grid 10 weeks in Alaska and a 2000 watt gas generator was enough to keep us charged up. Other than that we may do an occasional night or two in a Forest Service campground.
If you're 62 get yourself the Interagency Lifetime Senior Pass and a copy of Army Corps of Engineers Campground book.
Senior pass good for half off at Corps run parks as well as discounts at FS and other National Parks.
We also use free and cheap camping. Net. Most of these are small town or county parks some are very nice some just gravel lots.
Sometimes we are surprised by how nice a $5-10 FHU can be.
We volunteer 7-8 mos a year and travel the other months. We are on our 11th year full-time. Many don't last this long or they just zip to the same two spots one up North and one down South. Those that constantly move seem to get burned out after 2-4 years.
We enjoy volunteering I am a retired carpenter and wife is a birder and budding naturalist. We seek volunteer positions where our talents can best be used and we stay in beautiful places.
This are what we consider important for full-time traveling.