Not sure how the factory solar is wired, but shutting off the battery isolator switch should do the trick. See owners manual, the switch is located on the panel behind couch/bed slide-out drawer.
The battery boxes in our 03 Classic are made from a composite material but I still insulate the cables when removing the batts for the Winter. I occasionally plug into shore power with batts out so the insulation is more a precaution. I always go neg first, but remember you have two, so if you don't do both negs first, a short with one still connected will still cause a big surprise.
This is a useful item to keep 'em charged over the Winter...
BatteryMINDer Plus 12 Volt 1.3 Amp Battery Charger: BatteryMart.com
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