You could add some fuel stabilizer -- but for only a few months?
According to a Sta-bil website, " On average, the life of your typical gasoline is extended from 2 months oxidation life without STA-BIL up to 15 months will STA-BIL. STA-BIL keeps your gas fresh for quick starts... What Kind of Equipment Needs STA-BIL?
Any equipment that's not used often, or stored for 60 days or more, needs STA-BIL."
I'd put a tarp under the car for a moisture barrier since concrete "sweats", but then again, we're talking about 3 months.
Any mice issues? That can be a REAL problem.