If the generator is mostly going to be sitting around with infrequent usage, either go propane or research gas fuel stability and storage treatments.

Maintenance will depend on the model, but it’s going to need spark plugs and oil changes at a minimum.

When I looked at options for keeping a couple days worth of fuel around (with no gas-powered yard tools to necessitate fuel turnover), propane seemed like the more attractive option.

I was also storing said fuel in an outbuilding with venting and pretty far back on my property.

If you're regularly buying and storing gas, your math might math differently.