I have 4 12" earthquake LS subs going in my 2000 chevy extended cab truck. the box is 38w 26t 18.5d=8.79qf the port is 9.5tall 12 wide and 13.67 long. the box dosent sound good at all loud as hell in my shop but sounds like hell in my truck. i have more than enough power for these subs just could use some help with this. oh the subs are facing up vented out the front of the box.
the subs are older but new ive had them for a while. the vent tuning is 43 hertz
I have a crew cab with 4 12" alpin type r's and had the exact same problem - it sounded like garbage even with 3000 watts. I had a center port with the

subs around it like in the picture. It sounded best pointed up but still not very good.
My next box I built had the 4 12's along the bottom with 2 areo ports like the picture below

This box sounded much better than the last and sounded best pointed foward. The size was about 9cu.ft. net. I later shrunk it down to 7cu.ft. net, it lost some low end but picked up the high bass alot better.
I think what I would do if I was you is to build a box with the subs foward and one long port along the back top of the box. It may not follow the 7 to 1 rule with port dimensions but i've seen and heard it before and it sounded good. I would divide the box into 2 chambers, so 2 ports along the top back of the box.