kaptn,
I have been looking aggressively for the last year, have been in, under, and around numerous 5th wheels, trailers, and truck campers. The low build quality in even some very high $$$ rigs has really been a surprise to me. The industry continues to use vast amounts of particle board and OSB, which basically dissolve when wetted. Even the fiberglas "hard side" aluminum frame models are not immune to leaks, because most of them are constructed of vacu-bonded "sandwiches" with fiberglas on top of foam with a luan backing. This luan material is apparently identical to the "visible fibers" type of luan wood panels that are on cheaper residential doors and panelling. When the luan gets wet, there must be some sort of wicking action down the fibers because even a small leak at the top of the panel can cause delamination over appreciable distances - as the luan rots, it pulls away from the bond and the fiberglas gets a telltale "ripple" or bubble. The fiberglas / gel coat layer used in these panels is not very thick - about credit card thickness to 1/8" or so - and delamination can get ugly quick.
It is kind of sad to look at a high $$$$ 5th wheel in the $30K to $50K price range and see how the buyer gets shortchanged in places where the quality isn't obvious. Look under those fancy Corian countertops and in the cabinets you sometimes see particle board with the cabinet frames stapled on - and cheaply / poorly stapled at that. Or, when screws are used, it is distressingly common to find them driven in at angles such that they don't seat correctly, this is a by-product of the power drivers that we all use today. Under a cabinet, this practice isn't a big deal - but if it is a screw along a rubber seal area, and the cocked screw "bunches" up the rubber there will likely be a stress crack and leak before long.
Just about every used unit I have looked at has had water damage in one place or another, often the owners weren't even aware of it but you can find the stains on curtains, inside cabinets, and if rotted the "mushy" feel to the sides and corners is easy to detect. With this in mind, you would probably be best served by limiting your search to the best quality units in a given year and be prepared to pay a premium for one. It may cost as much to buy a top-quality used RV as a new lower-cost one, but you won't take a beating on the depreciation and you don't have the "unknowns" to worry about.
Note also that just because the '96 Fandabulous Qualidad had great quality and won many reviews does NOT mean the '98 variant will be just as good. Good reviews lead to increased orders, and often the manufacturers will start cutting corners to get more product out the door to grab the $$$ while they can.
Units that have impressed me: in the 5th wheel and trailer line, the Arctic Fox, Airstream, and Montana units looked very good. Note there was a visible difference between the West Coast built Arctic Fox and the ones I have seen from their East Coast plant (Virginia I think). In the truck camper world, the fiberglas Bigfoot (Canadian built) is the best I have seen so far, with Arctic Fox leading the US-made pack.
Note on Airstreams: You can find some SURPRISINGLY good shape Airstreams from the 70's, but boy those interior colors are REALLY something... . gotta have a strong constitution for some of them...
