@HiluxSurfBC I worked at RackNRoad in Seattle and we did riv-nut installs all the time!

We did 2 types of "custom" racks. 1st is using tracks (Most flexibility), and "hard point".

The nice thing about tracks is you can run them all the way front to back almost as far as you'd like.

Here's a link to Yakima (my prefered) tracks; 60” Tracks w/ CapNut Hardware

Step 1: Clean the roof (don't wax or anything)
Step 2: Lay down tape UNDER the where you want the tracks. Lay out the tracks how you want them (I went Parallel so that I can move the bars without adjusting the feet)
Step 3: Measure
Step 4: Tape the tracks in place on top of the tape.
Step 5: Measure them again
Step 6: Mark the holes (Tracks have holes every 6" - you don't need every single one - The first two, the last two and every other)
Step 7: Measure! (Make sure nothing has moved and the holes line up)
Step 8:COMMIT
Step 9: Center punch where you're going to drill.
Step 10: Get the propper drill bit and make sure it's sharp as hell! Also add a "limiter"- We used wine corks so that the drill bit can't go more than about 1/4 of an inch.

Warning: Be Prepared: the roof has bars in it and there's a good chance that you might hit one: if that happens the drill bit can RUN: go slow.

If that happens do not panic: there are alternatives to RIV nuts (name escapes me).

After you have all the holes drilled get your riv nuts ready and I also recommend some RTV sealant in each hole and stainless steel hardware. If you can, use a proper riv-nut tool.

Step 11: Riv-Nut time! Peel all the tape off the roof-line and go to town
Sealant to protect the edge of the drilled hole from corrosion
Riv-nut

Step 12: sealant in the rivnut
Step 13: lay the track on top
Step 14: LOSELY put the hardware in each riv-nut and then gradually tighten them all down to about 2-3nm.

Don't forget to add track hardware for the feet and don't forget to mount the end caps.

That's coming off the top of my head.

Hope that helps.