Nice! It’s a nice tool to have for non square drilling. Just add a mirror on a stand to make sure you’re aligned both ways

If it’s going to be in the shower, I can’t recommend MDF or even plywood. Probably better to go with solid wood if you can, or even better if you can access a 3D printer, use that.

The breaker panel is outside the shed (I understand this is by code) and low enough to be within reach of my son. I would prefer something inside the shed.

https://www.youtube.com/watch?v=Hg53x5W7YOc

The wood and plastic squares are super easy to adjust.

Yes, thanks! This is what I was imagining.

Looks like a fused disconnect is what I was looking for. Thanks!

That should work, thanks!

You don’t want the whole hemispherical cup. Just a semi circle.

The best and traditional tool for the job is a rasp. I recommend a Shinto rasp. Surprisingly fast and easy to use.