the sub or subs will be going under the rear seats in the ext cab if you know the 2000 gmc sierra you will know there isn't a lot of room so I will be limited in the subs I can use.

 

Are you going the prefab box route or are you going to be custom building the box for under the seats? Measure for available height, then take away space for the top and bottom of the box, then leave room so that the sub that you end up putting down there does not hit the bottom of the seat, then you are left with a max height of the sub that needs to fit there.

 

you are correct. also dont over look the titan line as well. they have the same guts as the brutus. the goliath, and other hifonic high end amps are monsters that are in most cases very under-rated.

 

I have enough room for subs with a mounting depth of 6 1/2 inches(give or take) any suggestions.