I have a travel trailer that I have camped in for the past 7 years. I know zip about popups. However, I just came across a 1997 Coleman Sun Ridge that is mint. The owner wants $2500. NADA book is $150...
Check all the canvas for rips, holes, mold, etc. Look for soft spots in the floor and crawl underneat to look for rotten wood. You should chock both sets of tires all the time, not just on an incline. If it's real steep, get some good chocks! Does this one have the one-piece ABS roof? If so, those had some problems also with sagging and I've seen a few that also had lots of very small cracks all over the place.