Trying to run two ported 10's under the rear seat of an ext cab chevy is going to be tough without lifting the seat, unless those 10's only need .75 airspace ported. Thise subs do best with 1.5cuft+ of airspace per sub. That box prob doesn't even have 1cuft of airspace to each chamber. I played this game with my box and several others and the only real way to do it is go sealed for the subs or do one sub ported so you can use the whole area for proper airspace. Best config I found so far is a single 12 ported under the seat using the whole area under the back seat. Sub up, port towards the door is how mine is and now I need to invest in dynomat because it is flexing and shaking everything from the windows to the roof.