When I look over a unit for sale on a pre-buy, I'm looking at the maintenance records for regular service. Oil, filters, chassis service, genny service. etc. There's a whole list of stuff that should be done every year, twice a year, every 24,000 miles etc. If the receipts for these are in a 3-ring binder in chronological order, I know that the current owner understands the meaning of preventative maintenance.
There's an entire generation out there that has not even lifted the hood of their car. PM means taking it to the dealer when the check engine light comes on. You can't treat a motor home or camping trailer that way.