I finally went and got some more MDF. Here is the horizontal portion of the frame. I was depending too much on my corner clamps, and had the workpiece try to lift during one of the drills, which is why you see filler on the one half. I’ll start throwing a screw or three through the middle portion if I do any more of this sort of cutting in the future.
I also (perhaps foolhardily) printed all of the 3d printed parts in one go, which took a bit over 18 hours on my machine. Electronics and hardware are still trickling in from China.