Use some sort of "float charger" (not a trickle charger) to keep your battery charge topped off. I use Battery Tender Plus, but there are many similar smart float chargers on the market. Do not start it unless you can drive it for at least 30 min. Just starting it will not allow the engine / exhaust system to get hot enough to drive off the water condensate which will not do either any good. You are better off just leaving it be. As far as fuel additive, a lot of folks use Stabil, I am not a big fan as I believe it does not do all it claims to do. Read your owners manual about your charging system to make sure about how to charge your batteries. Folks here will comment on other tips. Some people like to keep their car (tires) positioned on squares of carpet or other things to prevent tire flat spotting.