Wiring third brake light to Go Fast Camper

Anyone have experience wiring a third brake light on a truck cap to a rear taillight? Specifically a 2020 3rd gen Tacoma? I’ve watched lots of YouTube videos but it’s unclear the best place to fish the wires in. In some videos there’s a hole where I drew the x, in others it’s fished through a small opening in the bed floor (lower arrow). Also thought the opening on the side but then you could close it back up. Also the wires have are self tapping and have a fairly wide head. Any suggestions?

 

Drill a hole, spit on a grommet, push that thing home....wait, that's nasty, but true..lol
Zim

 

I used a flush mount SAE plug for my brake light. That way when the top is removed, there is not random wires hanging.

 

Nailed it!!!
Zim