I'm going retro with an old Pioneer KP-500 underdash cassette / FM radio.  I'll hide a RF modulated CD changer and Amp in the trunk.  A set of vintage Pioneer wedge speakers setting on the sail panel and it'll look old and still sound good.

P.G.

You can get a pair of old kick panels off of eBay, build them out with Fibreglass and wood, and mount a 6 inch (or 5 1/4) and a tweeter down by your feet.    Cover kickpanels with some kind of Fabric or even Vinyl to make it all look smooth.   Make a grill to cover the speakers and use acoustically transparent grill cloth for the grill.

The benefit is that you wont have as much PLD and your stereo will sound a lot better.   And you dont have to cut up expensive panels and look at ugly-arse speakers where there arent supposed to be any.

Besides when you go to a concert you FACE the music, you dont turn your back to it.  

 Human ears detect sounds left and right, but not up and down.  Therefore it doesnt matter that they are down by your feet, close your eyes and you cant tell. (unless your head is tilted sideways)

angle the speakers (mainly the tweeters) towards your "domelight" (obviously converts dont have one but pretend)  



heres the basics,

http://www.ritop.com/articles/csr9-98.htm


You can build a sub-box out of Fibreglass too(with MDF Braces). BUt it needs to be thick/rigid enough not to flex.  That is great in that you can maximize your use of space by closely conforming to the inside contours of your trunk to get the desired airspace behind your woofers.      

LB, I don't know if we're thinking of the same idea or not. I spoke with a friend of mine on the West coast and he put a system in a Challenger convertible. It's a Secret Audio SS system with the 10 disc CD changer. I believe he mounted the tuner/amp in the trunk, but he may have put it somewhere else. I know he put the CD changer in the trunk. He put a dual voice coil Custom Auto Sound speaker in the dash. He doesn't have a 3 speaker dash, so he mounted 5 1/4" rounds under the dash firing down and out of sight. Now for the interesting part. The Secret Audio system is nice but perhaps a bit underpowered for a convertible, especially considering the rear speaker placement. So, he mounted 2 200 watt amplifiers somewhere between the trunk and the back seat...not exactly sure where. For rear speakers he used 6 x 9 3 ways and mounted them inside the rear seat back near the top outer corners. Apparently it sounds great. This guy is meticulous like me so I take him at his word that the system is good. He has a friend that does professional installs and this guy basically did it for him.