Towing vehicle battery voltage drops to 10 volts overnight with camper RV plug attached and NOW shore power hookup

[Heckler45]

GOOD morning fellow rv owners. We have had two travel trailers in the past 20 years. This is our FIRST travel trailer with a 12 volt refrigerator/freezer system and a solar panel. I worked as an automotive technician for 32 years so I maintain all of my equipment like you wouldn't believe. We picked up our camper from the rv dealership (Refrigerator cooling issue) on Friday and I just left it parked in the driveway hooked up. I left the 7 pin rv plug attached and DID NOT hook up any shore power. I went to move the truck the next morning and the battery was low, I could tell by the sound it was making and thought "This isn't good." I checked the truck 12 volt battery and had 10 volts. My first thought was, of course the battery...but it's only 3 years old. I charged it overnight and it passed with flying colors. Then, I checked the alternator output....oh yeah, 100 amps and room to spare. Time to move on to a voltage/current draw.........I used my trusty Fluke 77 meter and nope, NO current draw other than the typical parasitic draw. I then remembered that the 7 pin rv vehicle plug has a 12 volt tab.......could the camper be drawing the vehicle battery down a few volts? So, I disconnected the shore power cord and backed up the truck to the camper. I had my wife watch the Fluke meter reading as I re-attached the 7 pin rv cord from the camper. There it is, the current draw increased to 1 amp. Has anyone else had this issue? We never had this issue with our last two campers.