The problem we find up here in BC is that snow and rain over the years will cause damage. I think the biggest issue is people that own these old rigs don't get up on the roof and change the caulking around vents etc...
When we first got married we had a 1978 Vangaurd Camper that we bought from a buddy that had a huge shop that he stored it in.
The first thing I did was crawl up on the roof and removed and replaces every bit of caulking on the roof, which even being stored inside was worn out cracking and falling off.
I also replaced the rubber weather stripping that covers the joint where the roof meets the wall.
Weather stripping That rubber weather stripping fits in a metal trim edge that runs along the joint between the roof and side walls. This rubber had shrunk over the years and exposed screws which if left open to the elements will allow water to enter the wood of the camper. This was probably the easiest thing to change as all I had to do was pull the old one out, heat up the new one on hot water and slide it in the groove. Leave about a foot hanging out each end for a day or two so the rubber weather stripping can shrink.
We had that camper for 5 seasons before we sold it and went with a 5er.
I saw the camper around town and the guy that bought it never took care of in and if a short few years it had fallen into disrepair and is now a hunk of junk in the guys back 40. We see it every time we drive by, sad.....:(
Your biggest issue with older campers of any type is roof damage. Go inside push you finger gently up against the ceiling looking for rott. Look on the roof, don't get on it. If there are any cracks in the caulking around any of the vents or anything that comes trough the roof, run away..... fast... who knows if water has gotten in and you can't feel it with your finger when you gently push on the ceiling... :E
If that rubber weather stripping on the edge of the roof / wall is missing.... run away... again fast! also look at where the camper jacks are bolted on the camper. If you see a thing that doesn't look right, stay away. I don't know how many times over the years I see or have heard of a camper jack bracket that had allowed water to seep in through the bolt holes and the wood rotted and the camper jack fell off when lifting the camper. Lucky most older campers you can lift the camper up using only three jacks, so the rig doesn't fall over. If you see a big glob on silicon covering the mounting bracket bolts on the camper.... run again.
Finding a good 30 + year old camper is hard to find around here but they do come up every now and then.
Fixing the rest of the camper is easy, but if that roof had leaked anywhere or those camper jacks have rotten wood behind them, your going to have troubles down the road.
Good luck
Soup