I love Volvo 240's.I had an '82 wagon that had no rear speakers. I built a couple free standing cabinets for it and a small sub. I always wanted to use the storage compartment in the center of the floor in the cargo space for a sub compartment. I think it's actually meant to be the footwell for the removable third seat. It seems large enough to do something with and you wouldn't have to remove anything when loading the car up. The space behind the passenger side rear fender had some good accessible open area. It seems like that space is very usable as well, especially after seeing a similar factory setup in the rear fender of an Audi A6. It was something like three four or five inch speakers.
I got rear ended in that car and the insurance company didn't think too much of it. Now I'm trying to put something together in a 240 coupe. What a great car.
charlie