I just went to a shop that installs car electronics and they cut out some 1/4" wood ones. They sprayed them with some coating. worked good. FYI getting to the rears is a major b****! you practically gut out everything from the seats to all rear plastics.
These speakers are ridiculous:
http://www.amazon.com/HCX-165-Hi-Ene.../dp/B003VCK7WK