I would put the 2x12 under your jacks and take as much weight as possible off your tires which are inflated to max pressure plus cover them. I'd replace the gas with non ethanol gas plus add SeaFoam even if I had to syphon the current out. If you cannot find non ethanol gas I'd fill a half tank of regular gas with AV gas. I'd put small solar battery charges on both sets of batteries and use the disconnect switches. Assuming the roof vents are covered, I'd leave them open and run the AC off the generator after every wet spell for an hour. I would only start the engine at six months and then let it idle in gear for 20+ minutes. I'd put a cup of bleach in the fresh water and circulate it. Spend the extra money on a silver tarp as it might make it for a year although it will probably blow off at some point.