I have a fleet of RVs. Class Cs, A gassers and A diesels. It is more expensive. For most maintenance items the diesel are easier to find a shop. You have one every 15 miles on a hwy and you can change oil, trans fluid, tires, alignments in some cases.
Gasses are a different thing. Although they are the same as a big van, they want to charge triple. Big shops don't want to work on them because they are too small or too big.
I do most of the maintenance. Diesel is more challenging, but worth it. Just find one that has been used with good maintenance records. 138k miles is on the low side. I have kept gassers over 300K miles with zero problems. That millage in that chassis is 13%of the life expectancy. The equivalent would be a car with 26k miles. Is that too many miles?