You'll live in it more hours than you'll drive it. Gas or diesel, go for a high end model (everyone makes entry level "weekend" models with interiors that won't hold up to full time use). If you need to tow over 5,000 pounds diesel is the only realistic option. Any engine can have a problem, but most don't! Rarely will the house part outlast the engine since the V-10 came on the scene. Maintained RV engines that fail are really, really rare. Gas trannys will probably need rebuild/replacement around 150k miles. All carry more fuel than your butt can sit in the seat.
Check to see what you lose access to when the slides are in.
If your choice takes you back to 8-10 old rigs consider that, while the chassis components, gas or diesel, will be mostly good (except belts, hoses) the reefer, furnace, a/c's, water heater, etc will be at or beyond "half life" so budget for replacements. Refrigerator replacement usually involves going through the windshield! Tires over 5 years are high risk.
Starting year 52 with over 400k miles of RV'ing.
