Basically, considering the space I have to work with, it would be best if I mounted the amp right to the enclosure. Is this really a bad idea? I do have extra MDF that I can secure to the back of the box and use that to mount the amp on. Input?
As long as your box is well built, and bolted to the floor it shouldn't be a problem. When you start to have problems is when you use a cheap premade box that doesn't have enough support, or bracing. When the box starts to flexes iridactly is when you will start to experiance problems. Not only can it hurt your amp, but you will loose SQ and SPL. Something else you can do is use a rubber spacer between the amp, and the box. It will help absorbe some of the minute vibrations.
Your idea for the extra peice of mdf is fine. You can even use a spacer to set it about 1/2 to 3/4 an inch off the sub box and run the wires behind it and bring them strait out and into the amp. Works really well if you want to hide your wires. Once you get it cut lay your amp on it and mark were you want the wires to come thru and connect to the amp. Drill your holes, then carpet and install.
the box is very sturdy (at least according to people i know in the audio business), and braced well (its a single chamber 28" across, so i was bracing it either way)
how do i know if i start to have problems? what should i look for?