You might try the white finer mesh 3M pads. Not the green ones, they can leave marks on the surface. I use the fine ones all the time on vinyl too and bought a huge box from Amazon for about $20. I cut them in eighths and just use a small section. It does take some elbow grease but are effective cleaning the grooves.
I love our short C but we do have the bed in the overhead. I think the smallest with a bed below is about 24'. You can get a corner bed in several older models but usually with only a dinette and chair, not a couch. I like having both a couch and a dinette in ours. I look at small RV layouts all the time and have yet to find one I really like. Probably the older sprinter Views and Navions are my favorite with the beds below and overhead. Some of them have a couch instead of a dinette.
The trucks are great because they are proven. Likely to be gas, either Ford, which is ours or the Chevy which is rarer. A bit of spark plug issue in the late 90 Fords--up to 2002 or so. Our is a 2002 and we have not had an issue. But I have read that the mechanics are used to the problem now and don't make the same mistakes made in the early years. Plugs aren't changed until 100,000 miles so really it is not an issue for most RV's.
I have no experience with any other type of RV but do really like our rig. Good luck with your search.
I think the Winnebagos (and Itascas) of any age are a good motorhome. Others may disagree. Their fiberglass roofs are less maintenance and I have not heard of one "peeling off" although anything can happen I guess.
Ours is newer (2003) and was more expensive and would still be more expensive I believe, more like 15,000 to 17,000. I would try for the 90's and not an 80's or especially 70's model. Prices are higher here in Colorado too I think. We bought ours when we lived in Arizona. More for sale and more older folks ready to part with one. But leaks in a Class C are a real problem and finding the damage from them can be difficult. Good luck with your search!
Fittings may be the same but all portable tank fillers cannot fill RV tanks. Our local rental store has a big tank but the can only fill portable tanks. Maybe it is the weight issue, I'm not sure. The "Next Exit" book shows if a gas station has propane on the road. One of our Ace locations and one UHaul has propane for RV's.