Used DP what to look for?

I'm not sure what you mean by extremely low miles but you might consider that with a diesel very low mileage might not be all that great. A coach that has been used a bit has had the "bugs" worked out of it and hasn't just sat around. If, for example, you may find a 2002 that with 35K miles but has been full timed for...say 10 years has had more stress than one with 100K that has spent most of the off season in covered storage.

In many respects the drive train isn't what sucks up $$$$ it's the ancillary equipment like fridge, awnings, flooring, upholstery, and other such items that are more "consumable".