Blow through box

My buddy is currently giving me 2 15" Kicker L7 for free because he doesnt want em. Ive decided I would like to put maybe one in my extended cab f250. But I want to keep my back seats but use a blow through box. Any ideas on how I would connect the back of the cab to the front of the bed?

you can use a campershell accordian rubber boot

That is how I did my blowthrough, with a camper accordian boot.

Yep, RV boot.