I know it's old, but very cool. recommendation for the cutouts (step 8):

Rather than cutting into the foam at an angle and guesstimating depth, you can make a clean cutout of the shape all the way through the foam. Then take the shape that you cut out and cut across it horizontally to get the right depth for sitting under whatever it will sit under. Then glue that shape back in place. You can get a more precise cutout that way with less effort.

Cheers on the very nice instructions!