I would not buy a new camper. My 845 camper model made by Lance had a retail price of $12K when it was first introduced. When mine was made in 2008 the retail price was close to $18k for the base model (AC, roof rack, 4-season windows, etc. add to that price). It was replaced a couple years later with the 855 that has a sales price of more than $24K. I bought the 845 used in 2011 for $12,000 instead of a new 855 which by the time I got it equipped at the same level as the 845 would have cost me $28,000 plus the additional sales tax.
I expect that when it comes time to sell the camper I will get about $10K for it and have a net loss with my additions to it of about $4,000. Had I bought a new 855 for $28K and added the same improvements as I did with the 845, and sold the 855 5 years later for $20K the cost of ownership would have been $10,000 and that is assuming that I could get $20K for a 5-year old 855 camper.
The only modification I made to the 845 that I would not have had to make to the 855 was adding a rack and wiring for a second battery. The other improvements, like adding solar panels and a controller, would have been done regardless.
The used campers in any given area depend in part on the brand. Lance campers are made in southern California so there are lots more used ones in this part of the country. I would expect to find more Arctic Fox campers and Wolf Creek campers in the Pacific Northwest. Where there are more used campers there are more to choose from and it is easier to find one that has been well cared for and lightly used.
If suprised me to read ads for used campers where people had never used the stove and in some cases never used the bathroom. Big difference between a camper used by a couple a couple weeks each year and one used by a family with children on most weekends in terms of wear and tear on the camper. In some parts of the country there is greater access to inside storage facilities and these campers will be in much better shape as a result. The worst are the ones stored outside in coastal areas.