To bring it full circle - y'all were right. The house batt was shot and disconnecting it - the drain went away with the isolator connected. As a bonus - the alternator seems to be alternating!
I may need to start a separate thread on this but - battery box. The old one is beat and I would like to put a new one. I see some posts say vent - some say don't worry about it (eg the Volkswagen that doesn't vent). I have a group 27 battery box sitting in my garage waiting for a home. It's vented on the sides but it doesn't direct the vent to the hose. Will this cause any problems?