I think I solved the "two things occupying the same space at the same time" problem

Performing some highly sophisticamated testing, it appears I have almost an inch of clearance

Good enough!
Cutting the angles was interesting. For the top, it just needed a slight bevel, which I accomplished with a jig and careful cutting to the line on the bandsaw

Cutting the lower front panel was trickier. I tried the same trick, but it was too much of an angle. The upper guide bearings on the bandsaw had to be raised too high and the blade flexed, creating more fire starter (from the scrap of AC plywood I experimented on before going to the expensive Baltic birch). I started to try sanding the required shape, but in the end the answer was the old fashioned 14 inch block plane. Did the job in four or five strokes.

Just a little tear-out from the inner two layers where I cut cross-grain. (I shoulda cut the other direction!) I'll fill the gaps in the end with wood putty.
Was thinking of reinforcing the front-top interface with a scrap of fiberglass inside the box, but it doesn't seem to need it. I used 3/8 x 3/8 inch spruce stock for most of the edges, with 3/4 inch pine where the PD 4045 and solar controller screws in. (Have to use wood screws as there is no way to reach back in to hold the nuts.)
Anyway, a bit of sanding, about 4 coats of varnish, and I can spend half a day getting the guts into the box.
Tom