Thanks all for the extremely useful advice.
Vic, Stan replied that FWC does not run wires within the frame members.
I've begun the process and drilled / mounted the rear set. It's a nice system that allows the rack to come on and off as needed, so it's there for surfboards or kayaks, but gone on for other trips, reducing drag and avoiding catching on low brush, etc.
https://www.rack-it....ts-184946-1.htm
It's bolted through (2 1/2 carriage bolts) and I used slightly smaller washers so they don't hang over the sides of the trim inside. A quick bit of tan paint and they're practically invisible.
Thanks again to our awesome FWC community for the help : )
Karl