I’m a firm believer in doing things correctly the first time, so you’re not cleaning up your own stupidity later. I’ve seen more terrible vehicle wiring jobs than I care to remember, usually involving sharp-edged holes drilled in firewalls, with thin-jacket cable and a disturbing lack of fuses. But damn, does that bass rattle the windows right off their tracks. It’s probably all worth it.
I used Bimed IP68 plastic cable glands to route my wires between the cab and bed. I had to drill holes in the bed to install them, which was unfortunate, but it’s all for The Greater Good. Take heed, guy with slammed WRX – use a proper step drill on sheet metal and you’ll avoid all those jagged triangular holes.
The ground strap provides a low-resistance connection between my house electrical and the chassis. I measured about a 1-2 ohm resistance between the bed and chassis before the strap, and 0.1 ohm (the lowest my Fluke can read) afterwards. The strap is connected to the bed with a bolt, with enough thread protruding into the bed to act as a main house negative terminal. The heat shrink is electrically unnecessary on the ground strap, but it adds some mechanical strength, and I just love heat shrink like you wouldn’t believe.