Your best bet is a generator for this. Make sure the battery disconnect has everything disconnected, which will reduce the amount of charging needed, and visit it every 1-3 months. You will need x number of hours a month of charging, so for example 2 hours once a month vs 4 hours every 2 months vs 6 hours every 3 months. When charging turn the disconnect switch on, an make sure everything still works. Depending on the size of the onboard charger, you may want to take a portable battery charger (the biggest you can run on your generator) and parallel them to reduce the time spent at storage.