There are a few overarching issues with specific models/years with Colemans and ABS roofs. There are a few gotchas on some other brands and models but it is so specific to mention brands and/or models to avoid is an exercise if futility.
If you find some specific models you are interested in, report back here with the details of each and see if we can line up any concerns about those.
The two most important factors when looking at used PUPs are the floor plan and the condition. When looking, I would look over the floor plan first to see if it would fit our wants and desires, then scrutinize the condition in many of the ways listed above.
Expect to replace the tires unless you have proof they are newer and the brakes, if equipped, and to touch up the caulking as needed.
Sit in them and run through having a rainy day and how the occupants will deal with it cooped up inside.
Buying used will save you some of the financial hit if your intention is to sell in the future.