the seat is heavier, but i built the box out of fiberglass so it is not all that heavy. i am sure if you built the box like sirGcal yours is much heavier than mine. also, my back seat has a quick release bar, so the seat still comes out fairly easy. i can just see someone pulling up and throwing the seat in the back of a car.
I dont have any pics of the amp rack yet i am not finished yet. although it was fairly simple. i used 1/4 inch mdf, i put a layer of fiberglass resin to waterproof and i plan on painting it. i bolted it up to the frame. i drilled holes for the wires to come through the back side. the cloth on the seat i just cut a slit down each side and i plan on having someone sew in some zippers to clean it up. right now i just have one amp but i plan on adding another and a portable hard drive. one of the keys is make sure you choose an effecient amp so there is no overheating issues. but the amp rack is great. with the sub box, no one can tell i have anything unless i have the stereo on or if the seat is flipped.