I scatched my head for a bit trying to figure out how to install my subs into the back of my Xfire without it looking cheap and still be able to get a couple bags of groceries (wife required that) in it and/or a couple backpacks - haven't tested either one yet (my 17 year old son is who actually drives it back and forth to school.) And the attached (hopefully) pics show the finished product that we completed in about a week.

Built the box with the correct cubic feet required for 10" MTX 5500's for a sealed box ( 0.75), barely got it to fit through the opening, and mounted it. Got cardboard and made a top template and a back template that went from one side to the other and conformed to the contoure. Traced the cardboard onto 3/8" plywood, cut them out, sprayed glue and stapled black felt onto plywood. Put in place, screwed the panels in, and re-mounted the amps. Finished product looks just about as good as I was hoping for.