I've just put two 5500 MTX 10's under my back seat. I had to build the box 57" wide, from one side to the other, to get as close as possible to the air space requirement. I used a 3" wide by 12" long port in each side. The speakers face down so the passengers arn't uncomfortable, and the ports face the back of the truck for added depth. I use a 600 watt class "d" mono block amp. They are very loud. I'm still under a week old so I havn't cranked them YET. But They are a perfect match for the four 6-1/2" component speakers i put in the doors. They are pushed by a 75 x 4 channel amp. I really like the clarity of the enitre system. But I think that two mid sized 10's are deffinetly a way to go.         &nb sp;         &nb sp;    

-Greg