This subject has been bounced around before and there are numerous opinions, here is mine,
You could add an Algaecide additive to the fuel if you wish, but I never bothered. I just made sure the fuel and propane tanks were full prior to storage to prevent condensation. Never had a problem.
Batteries, if you don't have access to a 15-20 Amp service, I suggest you remove the Negative Cable from each battery bank. House & Chassis.
By removing the negative cable you will completely isolate the the batteries so there is no parasitic draw to run them down. Check the water levels in each cell before you disconnect and top off as required. If you do add water, you must run the engine or generator for at least 3-4 hours to fully charge the batteries. Fully charged batteries will not freeze.
Then, I would go out every 6-8 weeks, hook up the cables and run the generator for a couple hours to fully charge the batteries and excersize the generator. Plug in a couple of 1500 Watt heaters while running the generator to provide some load and heat while you crack a beer or glass of wine and play a game of crib.
Dennis & Carol
2003, 4006, 41' DutchStar,
Spartan, ISC 8.3L W/BanksPower - 2013 Honda CRV, BlueOx Baseplate, Aventa Bar & Patriot Brake. And the 04 Bird, Sunshine Car.