I have a 2002 Lance 815, other than the refrigerator which would kill a battery in hours if left on 12 VDC, nothing else on that camper could drain your truck batteries as described.
1) Install a battery isolator as I did, under the sink where the Lance harness comes into the camper, it's easy to do it there.
I use a
Sure-Power
unit and it's been trouble free for years.
2) Find a reputable TC dealer and have Camping World work checked over, they most like messed it up. Personally I wouldn't trust CW with taking care of my dog!
