Air space???

[bigred90gt]

I have 2 kicker comp 10's that I want to build a box for to fit my 93 f-150 single cab. I need to know how much air space they need. Also if anyone knows what dimensions I could use for the box and not ride on the steering wheel, that would be greatly appreciated. I had them in individual boxes behind each seat, but I had about 4 inches between me and the wheel, and I don't think they had the airspace they need. I was running a 400 watt amp, it was all I had, and they sounded really bed. I took one of them out, bought a box to fit behind the center console where the speaker faces the back wall, and it doesn't sound any better. Same amp. The speaker(s) sound like they are bottoming out. I think it is an airspace problem, but I am no pro on systems. Thanks in advance.
Caymon