Best Under Seat Sub For 67-72's

[Blue/72]

So I am looking at pulling the seat and floormat out of my truck to install a sub or two along with applying raptor liner to the floor for in cab heat and noise reduction and I was wondering what the best sub you guys are using that will fit under the seat and give a good thump. I already have a dual kenwood speaker under the dash and pioneer kick panel speakers but they just don't have quite enough bass for me and I would like to get as much sound as I can without affecting the trucks body by doing things like cutting the dash and doors. Thanks in advance!