I've built that exact box for a friend w/ an AV12 and Rythmik 380 amp. It's extremely sturdy and amazingly well braced. You will need to cut into the back and the bracing if you plan on mounting your amp in the box. I finished the one I built w/ the PE Black Oak Vinyl because it was a spot on match for my friends Klipsch Refference speakers. If you go with the vinyl, put a couple of coats of black paint on all the edges so any imperfections in your vinyl work won't show up. Also, going over the edges w/ a router and flush will help get rid of any minor misalignments that could show through into the vinyl.
Painting MDF isn't easy. You need a good thick cover (not all one coat) of sanding sealer or else the MDF will soak up the paint, especially the edges. Also, sponge roled satin black latex has worked best for me, much better than anything i've ever tried to spray on. One trick I used on my first sub to cover where the edges soaked up the paint more was to make trim pieces out of stained hard wood.
Hope this helps
