No 12 V power at all W/O shore line or generator

If I remember correctly from my '04 Southwind the Main Battery switch is in the cabinet above the entry door. It operates a relay and there are two, one for house and the other for engine. It's been a while. Issue does not sound like it is related to the battery switches.

Fried batteries or bad converter/charger would be my call. Actually one caused the other most likely. Batteries are 2x6 V under entry steps converter/charger on mine was under the refrigerator and yes it was a simple one level.