Robert (the OP),
Using an extension cord, we leave our Class C plugged into a house outside wall receptacle all the time when it's at our home in storage.
Inside the RV we then plug a trickle charger's input power cord into a coach 120V AC receptacle on a coach wall near to the Ford cab.
We then plug the trickle charger's 12 volt output cable into a 12 volt receptacle on our E450's dash. These Ford dash receptacles are "hot" all the time - going directly to the Ford's 12 volt system.
This works very well to keep the chassis starting battery topped up all the time that the motorhome is plugged in at home.
