Dash pods

so, ive been tossing the thought around about some dash pods for a while now and was wondering what you guys think about methods of making them. The biggest issue i can come up with is matching the curvature of the dash where its going to sit. Tape and fiberglass? Some sort of hardening putty? I really like the idea of a 4" and a tweet facing the driver with the doors relegated for a midbass driver. Do folks use a DSP to drive the 4 and the tweet separately or a passive? i know that the pod will be a moderate undertaking to say the least, but the idea of speakers facing the listener sounds like a fare more effective way to get some decent sound quality as opposed to tweeters facing the driver and mids in the kicks or doors