I disagree on your cheap battery option. I would go to a golf cart shop and get a pair of GC2 6 volt batteries and install in series for 12V. You already have the space, they will tolerate being depleted to 50% or less much better and can last 8-10 years.
On solar, you can agonize over all the info and be paralyzed into inactivity, or you could just get a kit like this one:
Renogy 200w KitThe 100w panels should be small enough to wrangle onto your roof, but check the measurements to be sure.
And there is a good chance your local RV dealer might not know much more about solar than you do. At least with a kit, they will get some of it right. You are looking for a good solution with a small investment in time and money. The kit above should do it for you, but batteries are your first priority.
There is a lot of good info on this forum, and some members live and breathe solar setups, but that is not your goal.
