[Shop-talk] Aligning round tubing for mitering?

[Obaa]

Thanks for the suggestions!
I'm stuck using round tubing only because the current mounting brackets that the rack will attach to require 5/8" round tubing.  Since the minimum purchase was 12', I figure I might as well make the rest of the rack out of that size tubing...
I was looking for something similar to the clamps, but those blocks are too much $$$ for this project (the rack is to hold a bookbag onto a scooter).  I'm going to try simply tacking a small strip to the tubing such that it doesn't roll.  I'll then be able to make all the cuts relative to the plate.
The tubing is small enough that I should be able to get away with just using a large drill bit and press to notch the tubing.

Thanks!