Making more progress, guys...
As it turned out, I had miscalculated the number of sheets of MDF that I would need. Originally I only bought two, but later found out that I needed three. So last night I picked up another sheet and cut out the front piece of the box. From that, I cut out the 3 11 1/8" holes for the subs and sanded them down. I also bought some poly-fil to make up for the volume that will be lost when I finish bracing the box, and cut out a lot of the braces I will use. Home Depot did not have tee nuts long enough for mounting the subs, so I had to order them from McMaster-Carr. (That is a great supply company for hardware, if anyone does not know about it - cheap and very fast shipping) So those should be here by Thursday, perhaps Wednesday. I also ordered the sheet of plexiglass that will be used in the false floor to show off the amps.
I'm still on track for having the box put together completely no later than Thursday, and have the system in (might not have the top of the false floor finished, but everything will still work) by Saturday night. I'll post some new pics later on today or tomorrow.