Well I did some measuring after driving around a bit tonight and it looks like I can fit a tank that is 25" x 11" in the bottom part of the t-top holders (smaller part). Then I could make a new sub box that was fiberglassed from the upper part of the t-top holders and the little cubby to the drivers side. According to Sub Thump there is .6 Ft^3 in the cubby.
If I left it flat like it is now i might not have enough room, but If I angled the subs I could gain a little more(even tho I don't like that idea as much).
Here is the tank I'm thinking which is:
Length - 20.5"
Diameter - 9.5"
Height with legs - 11.5"
If I were to bend the brackets over a little I think it'd be short enough and then I could use 90 degree elbows out of the tank.
I think I need to find somewhere else to post some of this since it's getting away from carputers. . .