2020 Extrusion Outer Cover Joint

I needed to construct a frame for my Fresnel lens, which fits in the groove of the 2020 extrusion, so I designed these corners to allow that without obstructing the grooves on the inside of the frame.
Here's a simple joint designed to allow two 2020 extrusions to meet at a right angle. The holes are 4mm in diameter, so using screws and T lock nuts of 3mm or 4mm should be fine.
I'll probably design something better in the future, but here's this for now.
EDIT: The second file is a little bett