Drill a 2x10 as shown in the included drawing (or other 2 x X lumber as expedient) with 3 ¼ inch hole saw. Place inserts and place spray paint.

• 67pt5 file fits most spray paint, 68, 69, 70mm also included for use as needed. Note that this is the loose ID, which will become slightly smaller when inserted in wood structure.
• 3 ¼ in hole saw - https://amzn.to/3TlvqC9 [Amazon]

See my writing at: techadjacent.io

Inspired by holder seen here, but the outer walls of my garage are concrete, so I didn't want to put all kinds of holes in them.

*Amazon link is affiliate