Camper drawing on truck battery

Normal for GM trucks.
I like it set up this way. When I'm parked and the TC is plugged into shore power it keeps the truck's starting batteries charged up too. Even unplugged from shore, for that mater, my solar panel can keep my truck's batteries charged up. I use the 7 pin outlet (with a female cigarette lighter adapter) to power things sometimes and I don't have to turn on the key.
If I'm camping without hook ups and I think I may drain the battery I simply unplug the cord. It's not big deal.
If you want yours to always disconnect anyway I would install a voltage controlled relay. Then, when the camper or truck are charging they will charge all batteries. When there is no charge source the batteries will be isolated.

That is normal on GM trucks. I installed a relay on the feed line that is switched by a circuit that only comes on when the ignition is on. Truck off relay off. Did this on a 2006 and the current 2014. Glad I had it when the batteries in the camper died in Alaska last summer.

Yep , normal for a GM . I use a 100a continuous duty solenoid ( about 20 bucks )for the charge line . Hook the exciter wire to ignition only fuse , or always hot to a lighted switch on the dash so you can turn it on or off at will .

On my 2015 GMC Sierra 3500HD with 6 liter gas engine I have an optional auxiliary battery with a solenoid that is supposed to disconnect the starting battery so it doesn't run down.

Normal for charge wire to stay hot from truck battery on 2016 GMC 3500. Not one of GM's better ideas! I have owned 5 GM trucks since 1988 and never had one with factory ignition cutoff for charge wire. Your underhood fuse box on drivers side has a pink 30A fuse for that circuit. ( owners manual shows it) ..there should also be a 30A circuit breaker on that charge wire somewhere in your camper within 18" of where 7way plug enters. I plan to replace that circuit breaker with an accessable switchable breaker in my rig so I can cut truck off if I want to or when in storage. With solar I don't worry too much about running down truck batteries, but still want the choice without having to pull underhood fuse..

On my 2010 Ford I had to use a fuse and a relay that was found in the glovebox in an unmarked envelope before I could get 12VDC going to the trailer. The connection is only present when I have the truck ignition key on...

I guess the different brands of trucks all do it different...

On my Ford setup I also have a truck timer involved - maybe that is what you have too. When I turn my truck ignition key OFF and remove my keys the connection still stay connected for a couple more minutes. Then finally all of the truck interior lights and other 12VDC panel guages etc all shut down... This even happens when I have the trailer plugged into the truck 7-way connector. I lose all my trailer safety running lights when my ignition key is removed and times out. I wish that was on permanent. My older 2004 truck was that way. Someone told that may be an option setting in the truck electronics.

My truck 12VDC sockets go off after awhile as well when I remove my truck keys... I only have one 12VDC socket that stays hot all the time which is located inside my center console.

Roy Ken

It may be normal for your truck. Turning the TC battery off will only impact the 12 volts designed to be cut off. My slides still work, for instance. Can't say what on yours still would.

This recent thread has similar information about how to isolate your systems. http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29117358.cfm