How good are you with repairs? If you’re handy and plan to use the RV often, the 6.0 can be made reliable. I’ve done most of the work on mine myself—EGR, oil cooler, injectors, glow plugs, fuel pump, and more. It’s been an adventure, but it runs great now.
Go with the gas engine, or get ready to always smell diesel fuel.
I drove a U-Haul with a V10 across the country. It handled hills okay but needed full throttle to keep 75 mph. Got about 9-10 mpg overall.
The V10s do have some known spark plug issues, but those are still cheaper to fix than the common problems with the 6.0. For an RV that doesn’t get driven daily, I’d choose the V10.
I have a V10 in my 31-foot Class C RV and love it. It tows my heavy boat and trailer with ease, though the transmission can get hot on steep climbs, so I’m adding a trans cooler. It’s a gas guzzler but super reliable for RV use. I’d go with the V10 for your situation.