I would say depending on where you live and the tempratures are, you may be able to get away with all electic. Definitly if you are not using the climate control it will be alot easier to say in all electric. I will say even when I had the climate control off, the engine did still run occassionally so I a not sure it woud be possible to stay completely on EV all the time.
In Canada, I use Gas Stabilizer, for things like our lawn mower, snow blower, etc. It extends the life of the gas to 6 months. I did have a mechanic tell me that gas does not go bad but then my father always told me it does. Take your pick of which one to believe.