I'm mulling a 2nd bus, redesigned for my current needs, and truthfully considered the same thing you are. I was looking for a decent bus that was cheap and gas powered, as most of your modern gas engines are decent little runners and gas powered onans are a dime a dozen and much quieter compared to diesel units. Then I looked into used JH uhaul's and a truck bed camper, as that would likely suit my needs too, and be way heavier built then a 1 ton truck. I'm not a fan of juice brakes on something heavy, how they're all equipped with low-pro tires, and I definitely have an uneasy feeling about buying a former rental vehicle. In my experience no one every drives a rental gently. Tires are something that can be fixed, and brakes are something I could get used to, but the whole rode-hard-and-put-away-wet treatment is something IDK I could overlook.
Like you, I'm nervous about their rating system. A lot of the ones give the engine a 2 star rating. IMO that means serious engine damage that needs addressed immediately, which renders the truck near scrap. A lot of the cheap ones have issues, typically engine issues, which is odd to me as the 8.1 and ford v10 are usually reliable runners in my experience. Talking to some of the guys at the service centers, they do fairly decent and thorough maintenance, but I feel they view spark plugs as a repair item and not a maintenance item. So I don't believe they touch spark plugs on these things, and at at 160k they'd way overdue for spark plugs and a good tune up.
That'd be a pretty easy fix if that all one would need. I still might do it and take the risk.
BTW uhaul hasn't bought a diesel unit in 20+ years. Several reasons for it, cheaper initial purchase price, commonality across the fleet, gas engines being cheaper to service, etc..... But the biggest reason is that they had too many roadside visits with people putting gas in the diesel tank. Gas being cheaper then diesel(people biased towards using cheap on something they don't own) and the general naivety of the general public(people are clueless), I would never have a diesel rental anything. People are habitual, and do stuff without thinking. We had 1 gas bus in the 2000's as a spare, and once a year a driver would put diesel in it by mistake, even though it had "GASOLINE ONLY" in big black letters above the fuel door. Sometimes it's easier to design things around the lowest denominator, then it is to struggle against it.
FWIW, if you didn't know, adding diesel to a gas truck is somewhat inconsequential, with the worst requiring you to drain the tank, purge the system, and refill it with fresh gas. Whereas gas in a diesel truck is typically catastrophic, and requires thousands spent on injection pumps/injectors and flushing the fuel system. We get a call into the shop every now and again where a customer does just that. In my experience you can mess up and add a few gallons of diesel to a gas truck and you'll likely notice no issues. Maybe a little rough running, but that'd be fixed at the next fill up. If someone calls in because they added gas to a diesel, I'd recommend towing the vehicle and flushing the tank.