Total winter here in Ontario. Had 29D Jayco Melbourne for 7 winters. 1/2 hour to winterize, remove battery.
Started 1st time, everytime, in spring. 6.8l Ford V10. Religious maintenance always, with any complex vehicle.
Now we have a 40 'DP , different animal all together from gas. Trickle charge all batteries (maintaining water) after winterizing of course .
Run engine, genset, 1/2 hr every month. Been OK for 3 years so far, and even more religious with maintenance.
Remember, total lubing and tightening, dielectric grease, etc , , minimum once a year.
50 years gearhead and backyard mechanic.