I have a 2012 Winnebago Itasca. I bought all new Interstate battery in February, took the coach to Florida for 7 weeks without battery issues. All seven weeks we were plugged into shore power with ...
Wait. The chassis was shut down for 7 weeks. Most rigs I know will not be charging the chassis batteries while plugged into shore power. That's when you use the battery "instant switch" to get her going, then drive around to charge it up.
Or run a Trickle-Charger on the chassis battery while shut down.