Hello there and welcome!
Sorry, I saw your post too late to offer information before you took a look at the unit this past weekend.
However, when I looked at ours I did not notice rot in the rear floor and believed the seller when he told me there was none. It might have been an honest omission of a detail he was unaware of, who knows?
Its pretty much a given that you will need to replace window gaskets/seals.
Check for leaks around all the pipe joints.
Mold in the carpet.
Has carpet been replaced and what with? If so, can you find out what the floor was like? Does it give a little/lot when you walk on it?
Ensure all the systems work. Again, I was told everything was good on ours but found that the Town supply intake was not connected and neither was the power. I didn't pick those two things up when I inspected because I really didn't know what I was looking at (if that makes sense) This was our first ever trailer.
When I find another one I will be much better prepared.
Check the torsion bars on the axles, you will want to replace them regardless of what you are told. Do a search on the site for more info.
Best of luck
A wise man once told me he wanted to stay fit enough to run a marathon on his hundredth birthday. Another said he wanted to be shot by a jealous husband on his, I'm with the latter. God bless you Richard.
Carpet Cleaning is what I do, it's not who I am.