To me, the toughest part of notching tubing is getting both of the ends notched square (or whatever the exact angle is that you want for that intersect), and getting both notches in line with one another on one length of tubing. I normally use 2 drill press vises on a flat surface to clamp my workpiece, then remove one of the vises so that the setup fits on the drill press table.

However, it still seems like a chore to keep things aligned, level, and straight! In reality, I just need to build more clamps and fixtures as I see a need for them, and work in a few degree wheels for accuracy.

Using tools I have, to build tools I need, just so I have what I need to create actual (non tool related) projects. That's just swell.