After having owned all 3 types, gas, diesel and now propane, it's not that big a deal with the propane, no liquids there except the lubricating oil.
Now the diesel and gas are a different story, especially the gas one. Even if you put Stabil or whatever you use, the gas starts going bad right away and creating a gum up situation in the carb.
On our gas one I'd run it for about an hour every 6 weeks with a load and no issues after 3 years. The diesel one I did the same, maybe running it a bit less. Both tanks were loaded up with plenty of fuel treatment in the late fall, and I always filled the gas one with straight gas, not ethanol mix on the last fillup. The diesel I filled with straight diesel, not bio.
Our current propane unit only gets started and run when we need it, and after 2 years, no issues.
Yes I realize Onan says to maintain the warranty, this needs to be done....
Bob & Sharon
Eastern Kansas
2013 Winnebago ERA 70A
Class B Van