Yup, the -only- thing that charges a friend Monaco is the engine. Try the cross-connect to the house batteries and start the engine
BTW, leaving your rig parked all winter is really hard on it. You should, at least, start it every month and let it run for a time. Better is take it for a 15 to 30 minute drive.
2008 F350SD V10 with an 2012 Arctic Fox 29-5E
When someone tells you to buy the same rig they own, listen, they might be right. When they tell you to buy a different rig then they own, really pay attention, they probably know something you don't.