Why not do fiberglass? It's so much easier and usually better results than trying to put together MDF box inside that tiny trunk. Here's a few pics of one I made for my work truck. Nice thing too is that you can tailor the size needed for the subs. Remember guys anyone can build an enclosure but only those that know what they are doing can make one with the correct volume of space needed for the subs AND car.
masked off area
layers of resin only.
Layers of resin with one layer of matting with front cover installed
Back view of reinforcements
picture with rubber coating inside to dampen unwanted vibrations
completed tiny box installed