Update to this issue..
Another extended period of no use and another dead battery but this time no key in the ignition. No obvious things left on to account for the drain. The idea of through switch is not practical to me for many reasons but mostly for where the battery is located and a visit to a Mercedes dealer is not very appealing either although that will be my last resort.
So again this is the chassis battery not the coach (Compass 24 TF) batteries and during this last period the coach was on shore power the whole time. I guess first question is how do I determine IF there is a drain when everything is off? and second how would you determine what it was?
If I see no drain then I guess I would focus on the battery itself? Thanks again for any feed back on this