Generally they’ll last around 20 years. After that the only people who will insure appear to be the Caravan Club.
Seals and mastic start to go at 15 years + but there are plenty of fix it websites out there and modern materials make them an easy repair. I bought ours as a ‘spares or repairs’ 1991 Fleetwood Garland all the gear and a giant awning with a leaking window (did the repair myself – £40) Cost was only £700 for a caravan I could now flog for £1500 at least.
If your looking to buy an older one look take a cheap damp meter along and have a good prod around – window seals are a favourite spot, as is wheel arches and around the awning rail.
If you need anymore help let me know.
BTW contrary to popular believe they’re a good holiday especially for the little Huns. Why bother with a tent and buy all the crap to go with it when you can get vfm like that?
TS