This is a good-better-best kind of discussion. The very best practice may not yield any better results than the least best, depending on the conditions.
Odds are the coach battery disconnect switch does not totally disconnect all loads. CO or LP detectors often remain connected, leveling jacks & slide motors may also be powered (though not necessarily drawing noticeable current). Physically removing the battery ground terminal wire will absolutely prevent any of that stuff from drawing current.
The batteries will self-discharge are a VERY slow rate if all loads are off, so they probably remain above 50% charge (12.0v) for 5-6 months. If so, there is little need to run the engine or the generator to recharge in the interim. Ideally the batteries should stay above 12.4v, which is about 80% charge. Whether yours will stay that high is something that only experience will tell.
A battery at 40% charge (about 11.9v) will freeze at 5 F., so you are on the hairy edge if the battery voltage drops to 50%. This tech article from Trojan Battery may help you out.