If it's a gas engine: add fuel stabilizer to it, and run both it and your generator to get it up into their fuel systems.
I used to like to run Stabil in mine.
If you use fuels with ethanol: they have a blend for that situation.
Good Sam Member 843599689
Current coach: Tiffin Wayfarer 24 BW
"History shows again and again; how Nature points out the folly of Man!"
2nd on the Seafoam. I put 3 cans in a full 80 gallon tank, drive MH a few miles to get into system. Get home run genny with load for 1/2 hour to get treated fuel into that system. Run V-10 and genny 1/2 hour every 4-6 weeks while stored. I keep my rig plugged in and battery switch in use.