My Lance 815 is running down my truck batteries- any tips?

I have a 2001 Lance Lite 815 and a 1993 Chevy K3500 TD. Ever since the TC install a few months ago, the camper runs down the batteries in the truck (it has 2), but the only thing on the draw is a carbon monoxide detector with a little green light that stays on. Is that really causing the batteries to drain down after a few days or what else could it be? Lights, fridge, anything else electric is off.

I've added a solar battery tender on the dash (good southern exposure daily) but it seems to do little to help. I'm also wondering where I can find a Y-adaptor to hook two of them up in series to see if that helps. Until then, I have a traditional AC tender on there that keeps them topped up temporarily but don't want the cord hassle (kids). Thanks!

P.s.: possibly helpful info, also post-install, it's blowing my turn signal circuit. Replacing the fuses helps for one drive, but then they blow. Adding a heavy duty turn signal relay didn't help, and actually it won't work at all now even with the original relay, and the fuse is now staying good. The reverse lights are also on this circuit and I know one is out, but I can't imagine that causing this much trouble (hard to get at that assembly now, will have to dismount the camper to change that bulb!).