I screwed directly into the plastic (PETG, 90% infill). This works ok here, has worked ok for most designs I've done. If you're designing a new one, maybe sink (or side-slot) some nuts in there, sure. The plastic threading hasn't caused any issues in this case. It's just that I noticed the threads weren't the strongest when I tried to snug the screws up after using it for a while.

What did you screw the extruder bracket bolts into? Is there a nut sunk underneath?

You're welcome. Mine's been working great since I printed the final (pictured, above). Two changes I'd make: 1. Shrink the extruder plate mounting holes just a teense - they could grab the screws a little more firmly. 2. Provide sure support beneath the stepper motor. Probably a bunch of trial-and-error there, but right now, the motor floats just a little. Good luck with your design!

thanks for sharing this, the other popular relocator design online looks ridiculous and is set up at a really awkward position. I was wondering why they designed it that way (mostly to avoid buying an extender cable I believe). I'm designing my own, and this just proved that my concept is feasible