Delam is only an obvious indication of a greater issue. Nobody wants water intrusion into their camper. Nobody wants mold in their camper. That's what it needs to be maintained with yearly inspections and resealing of the roof and wall joints. Azdel does not change the fact that maintenance is required it just makes neglect less obvious.
If you are seeing delam that is typically a sign of poor care for critical maintenance.. I wouldn't buy a used camper that hasn't been maintained. On the other hand a camper that has been well cared for and stored out of the elements can be a great buy even if it has luan laminated walls.