I try to avoid the issue, largely because motor caravans and campers are built on LCV chassis designed to do 300,000 miles in 6 years, then be scrapped. They aren't designed to do 4,000 miles a year for 15 years, and sit under a tarp on someone's driveway right through each winter. The best basic advice I can give you is, for the same money, always buy newer and higher mileage rather than older and lower mileage.