Hi Duane,
I'm familiar with those vents. And your idea is a good one. I've inserted grommets from the inside (current truck) and I've used removable plates that are below the cab to get inside with wiring.
I "think" I am okay for wiring in my current build plan
BTW, and I'll put up a link and pic later, borrowing on something TerryH did in his new truck, I'm having CC install a device I sent them. It's an ignition sensing timer based power distribution block. It will be fused and wired hot plus wired to an ignition switched supply for the relay in it. It has DIP switches to program the timer. It has 6 screw lug outputs each capable of 5 amps of current and each output fused on the block with small blade fuses.
I've asked for this to be mounted in the cab to the firewall, behind the brake pedal or nearby. Initially, I'll be using it to power the feeds to the TPMS receiver, the backup camera monitor/receiver and the Koolatron cooler.
I'll program it to shut down power 2 hours after the ignition is turned off.
Jim