4.7 ground locations in rear

Hooking up a second battery for camping and future accessories. I have it where the spare tire used to be in the rear. Anybody have any recs on places to run the ground wire back to or will any part of the chassis do? Running a ground wire all the way back up to the engine bay seems unnecessary.

BTW the system I have set up is I have a diehard gold battery as my primary battery, it’s done really well in the cold. That is hooked up to a blue sea systems battery isolator which I have drilled an empty spot in the engine bay and it’s tucked back there nice and clean. Right now I have the wire running from the isolator to the positive terminal of my AMG deep cycle battery, and it’s routed down next to the brake and fuel lines on the opposite side from the exhaust, all wrapped in wire loom and e tape. Only cutting I’ll have to do will be thru the old spare wheel well which is nice.