Solenoid installation inline with trailer plug hot wire

[Iceworm]

I have a 2017 Sierra 3500 All Terrain with factory trailer pkg. plug/wiring.  I would like to install a continuous duty solenoid inline with the trailer hot wire (red-green wire)so when my camper is plugged into the truck plug the hot-wire is energized only when the ignition is on.  I don't want to drain the truck battery when using the camper battery while camping but still want to charge the camper battery while driving.  I wired this system in on my 2003 Duramax and would like to do similar on the 2017.  The '03 had a stud at the fuse block to use.  Where can I access the trailer hot-wire near the under-hood fuse block to connect inline with the solenoid and where can I hook into an ignition powered wire for the solenoid.  Thanks