With any camper that age, signs of water damage is going to be the big thing. There may also be water you can't see or smell a moisture meter is a good investment when shopping for a used camper.
Our T264SR had water in the back above the cabinet in the bathroom and ran down the back wall, the rear roof seam seal had failed. It also had an older water damage above the bedroom overhead cabinet, the front roof seam seal failed, but was resealed, the wood dried out over time but was dry rotten. If possible look at the roof for signs of ponding water and aged/split caulk. The roof is not walkable. It should have some give when you press your hand, but if it's springy like pushing on a balloon the membrane substructure has been water damaged.
Not to possibly scare you away from buying, it's a really well-built camper, and all can be fixed.
This is the repair of ours. The beginning is the inspection of what we found, shows how it's built.
Current Camper: 2006 Sunline T-264SR
Previous Camper: 1998 Coleman Mesa
Tow Vehicle: 2002 Chevrolet Avalanche 2500, 8.1L, 4X4
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