The speakers are usually too low for good sound in that location. If you just want some sound and aren't picky about how clear the sound is, they are fine. I think Rod Doors has a kickpanel setup also.

You would probably be better off with a behind-the-seat all in one triangular speaker box, with a single woofer and upward firing tweeters (usually a horn of some kind) - as long as the gas tank is out of the cab. You can place some small dome tweeters on the dash to fill out the high ranges.