I would say 4K is probably what's it's worth with or with out the issues it has because of its age.. If you put in the time and money to fix it up you won't be making it worth any more just more appealing. If there's no water damage in the corners or rotted flooring it sounds like a nice project I've fixed a floor in a slide the sides were rotted about a foot in on both sides because of bad caulking on the trim that wasn't delt with. The wall was fine we ripped up carpet and cut the rotted wood out and replaced insulation quick fix then laid out sticky tile but the right way is to pull the slide out and repair it depending on your intensions. I wouldn't mess with anything with rotted flooring or soft corners A lot of hassle . The problem with slides is the fiberglass doesn't hang below the floor it stops right after the trim so when not maintained and it leaks it goes and soaks right into the floor.. If everyone maintained there rvs like your suppose to no used ones would of water damage. I know a guy will an 94 TT thing is clean as a whistle owned since new I bet him 50 bucks i could find a leak or water damage but I didn't never seen an rv that old that had no weird smells and the condition of the roof is unbelievable.
Rich,242014 wildwood 27RLSS travel trailer
2005 Chevy Silverado 2500HD crew cab
2005 GMC Sierra 3500 single cab dump