Pretty sure that battery cutoff switch near the house batts in the rear PS compartment is for house batts only. I donít think gas coaches have chassis batt cutoff switches.
Pull the negative cable off the batt under the hood. Ensure you insulate that cable while unattached so no unintended nasty nastyís occur.
2019 Tiffin Allegro Open Road 32 SA.
2016 Subaru Crosstrek.
2004 Lazy Daze Class C (sold)