I've been looking at adding a power plug to the cargo my '17 TRDORP. It doesn't need to be crazy big. The max draw I'm looking at is around 15a with an average of 12a - 13a.

I saw the stock plug is rated for 10a. I thought about using and rolling the dice, but I keep talking myself out of it. I also really don't want to tear my truck apart just to add a single plug wired back to the battery.

I've not had time to remove the cover over the inverter/wheel well. I'm assuming there is a decent gage wire going back to the inverter. I was thinking I could Posi-Tap the wires and add an SAE (Battery Tender style) or Anderson Power dongle.

Has anyone done this or looked into it?
Does the inverter dash switch control the DC feed to the inverter?

Posi-Tap
Posi-Tap- No Crimp Tap

run a wire, it will take you less than 10 minutes. the door sills pop right off, you don't have to tear anything apart.

I second this and while running it I would probably do a 6 or 8 gauge. That way if you decide later to add more plugs or accessories back there you can add in a bluesea fuse panel and youre set. The wiring to the factory 12v receptacle back there is insufficient to run a fridge efficiently. They typically have a low voltage cut off to protect the starting battery but theres enough voltage drop in the wire run to set it off prematurely. I ran a separate always on line and receptacle for that purpose.

I've run a small wire through the grommet behind the e-brake, but that was just for something under the dash.

Is there an easy path to reach the rear cargo area and place the fuse block?

There are grommets on both sides, feed through one of those and then in the existing wire raceway in the door sills to the rear. The door sills pop right off, to get from the back door to the rear wheel well you can use a metal coat hanger to fish the wire.