OK, I'm not looking to shake all the screws loose in my 71 chevelle convertible but I like decent base.
I currently have a four speaker system: I have 2 six & half inch
Infinity speakers in the kick panels and 2 six and half inch Boston Acoustics (because of their compact magnets) in the cylinder covers in the rear.

The system is clear, but is lacking base. and doesn't look obnoxious (all the grilles, surrounds, etc are satin black and blend in fairly well).
The holes for these speakers were cut before I purchased the car.

I don't want to give up any trunk space. Mounting 6x9s in the stock position really wouldn't give me the sound I want.
I thought I read about someone making use of the area between the well and the back seat for a sub enclosure.
Just a couple 8 inch subs would surely give me the sound I''m looking for.
Has anyone done this to their 68-72 chevelle?
Thanks!

Your setup sounds a lot like mine. Some people have used that place when making complete trunk boxes and incorporating the speaker, but my issue with doing that in a convertible is losing access to the pump and / or lines should it leak. For now I have a JL 10w6 in a sealed box just sitting in the trunk, but whenever I get around to finishing the trunk I'm thinking of putting one 8w7 in the side area with the cone facing inside and the magnet pointing toward the fender.
http://cgi.ebay.com/ebaymotors/68-69-70-71-72-CHEVELLE-TRUNK-PANEL-KIT-_W0QQcmdZViewItemQQhashZitem27b366a420QQitemZ17051 3572896QQptZVintageQ5fCarQ5fTruckQ5fPartsQ5fAccess ories

While this in no way seems worth $400 to me, especially when the seller says he will not respond to email questions (which to me says 'nothing in writing') this looks like it could be made to hold a speaker or two somewhere. No clue what it's made of though or how sturdy it is.

That ebay kit looks like what I would do eventually and have the subs to the sides in sealed boxes(10in not tini 8s)but for the $400 that's being asked for that one I could get enough pdf and fabric to do 40 cars.How hard is it to make a cardboard template?Whatever that guys smoking he needs to start selling that instead.

I really don't want to loose any trunk space (even the side). Just to keep things simple I'm thinking of mounting a couple 6.5 inch JL subs where the factory 6x9 cut outs are and making enclosures in the space behind them. The JL 6.5 get really good reviews by other guys with limited space vehicles.
That way, my top pump stays where it is. and everything else can stay where it is.
I'm not looking to wake up the neighborhood. I've got a powered 6.5 bazooka tube in the trunk of my daily driver and it really sounds good. Not thundering like the 10 in abox in my pick-up, but defintely good!