I'm sorry, but you are not going to want to read this. We live on the wet coast. It rains here. The siding isn't a problem. The caulking is. Butyl tape is used because it's cheap, easy to use, quick and makes a good looking job. It just doesn't keep water out. Which is a good thing for the industry, a trailer will rot out in about five years ,about the same time as your payments last.
A RV can be leak free for about 20 years. Ours should out last me. I've even been accused of turning my camper into a submarine. The leaks are at the corners, sidewall/roof, windows, doors. The answer is simple. Quality sealant like Proflex or Stikaflex for walls and Dicor self lapping for roof openings. The stuff is about $15 a tube here. And you'll need a carton or more.
My Missus and I did the TT in two weekends. It's work, and messy work to boot.
It should be done within a couple of years of purchase. A simple check is to pull the vinyl trim, it just snaps out, and undo a rusty headed screw, if it's got rusty threads it's time.
