Between-overhaul mileage of a well maintained RV gas engine?

With today's synthetic lubricants and good maintenance (including keeping the cooling system in good condition), there is no reason a V10 or 8.1 won't go 200,000 miles. At 7,500 miles per year, the house part will be falling apart first.

Actually, thinking about it a little more, the age of the engine (gas or diesel) may be the bigger issue. Rubber, electrical, and plastic parts get tired after 10-20 years.