We have had four 5th wheels and the last 2 were bought new. We prefer new. No one but us has
used everything in our new 5th wheel.
When buying new , check out how much formaldehyde is used in building of some brands.
We never had any problems with this in either of our new 5th wheels. Some entry level brands use so much it is hard to use those trailers until they have been aired out or used a few years.
Do not go for the asking price!!! Especially a used one....make them an offer and if they say no! Be prepared to walk away. Most of the time they will call you with a lower price than what originally was given. I have done this on last 2 trucks and SUV we have bought.