I've never known of any asbestos products being used in RV construction, at least in modern times. There have been problems at times with some of the paneling products outgassing and causing respiratory issues, but the common fix for that is ventilation and time. I would really be surprised to find a 20 year old RV having that problem. A more common problem in older RV's is mold in the walls and/or cabinets, usually related to water leaks that may not be very obvious. Mold spores of course, can cause respiratory problems. There are tests for mold presence, but I'm not familiar with them. It's not something a dealer would likely test for.