Dead batteries in 04 Duramax 3500

Question for all the savvy after market wireless back up camera users. Installed Garmin GPS unit that has bluetooth and also back up camera that came packaged with it. Wired it to constant hot to be able to check on trailers when pulling and set it up with a plug-in at the bumper to be able to disconnect easily when removing camper. My question is, does the camera and transmitter draw power, I know there is power TO that stuff, but does it DRAW any from the battery is not being used and cab GPS unit unplugged? IF the old Duramax sits for a week the batteries go dead. Bells and whistles work just won't start. Am checking the interior light door switches and the glow plug switch as well. The camper is totally disconnected from the truck when parked as I Haven't gotten a switch installed to turn of gas leak detector. We've had this 04 model truck since December 2003 and this problem just started in May of this year. Only did it once at that until today. Hadn't been driven in two weeks since getting the bumper fixed from deer collision and getting the blue tank bracket mounted. May be needing to get new batteries, they're 2012s?, wet cell replacements on list and dual battery trickle charger as well for future. OK guys, it's open season now, go for it!