Ours was on AirForums Classifieds and Ebay I think. My only advise to you is "BE ABLE TO REACH OUT AND TOUCH IT"
Pick something thats no more than a weekend away or better yet a few hrs drive. Go inspect it in person. There are people here that can do a preliminary volunteer inspection for you,but the final is up to U. There are people here with tips on what to look for,what models to stay away from ,where to look for the trouble spots.
GOOD LUCK ON YOUR SEARCH
Roger & MaryLou
F350 CREWCAB SW LONG BED
7.3 liter Power Stroke Diesel
1977 27ft OVERLANDER
AIR # 22336 TAC- OH-7
May your roads be straight and smooth and may you always have a tailwind!