If you have the batteries disconnected, and fully charged, they will be fine for 7 months.
Otherwise, You can get something like a 100 watt portable panel with a simple charge controller. Set the panel on the roof and secure it with something to keep it from blowing off. That should keep them topped up.
Happy Glamping.Norman, 2008 Winnebago Adventurer 38J, W24, dozens of small thirsty ponies. Retired after 40 years wrenching on trucks! 2010 Ford Ranger toad with bicycles or KLR 650 in the back. Easy to spot an RVer, they always walk around with a screwdriver or wrench in one hand!