Duramax batteries drained by camper while plugged in.

GM trucks have nothing to disconnect the camper batteries from the truck batteries. They are constantly hooked together as long as the 7 pin plug from the camper is plugged into the trailer. The solution is to unplug the cord from the truck when dry camping. Or, you can install a switch in the charge line and turn that off. If you want to automate the process I would install an automatic charge relay from Blue Sea systems or another reputable brand.