Tom Del Rosso wrote:
Here is a rough diagram of the cross-section as I envision it. The back
needs to overhang a 1.5" bulge in the wall.

Maybe the structure could be improved. I appreciate any input.

Would work, but could be simpler.

I'd go with a large top box and a smaller bottom box. Same amount of
work overall, but it gives a bit more support for the front. Probably
no need for the diagonal--just screw the box to the wall and the floor.

Chris