there are two ways
cut a false floor 10mm smaller than needed with the hole for a sub above the well (cut the sub hole around 10mm-12mm bigger than needed)
stick masking tape all over the wheel well and up onto the top of the false floor 3" beyond the edge of the hole, (keep the tape tight over the wheel anchor or you'll not get the box out afterwards)
cover the tape with fiberglass matting and resin around 3 inches past where the masking tapefinishes on the top of the floor, (at least 2 layers) leave to harden between coats and........
"hey presto" you have a box
remove all this from the car
line the inside of the box and about 10-12 inches onto the top of the false floor with dynamat to cover where the resin finishes,
lay thin foam 3-4mm on the false floor and cover with carpet to match the boot
put a layer of thin foam 3-4 mm in the wheel well and refit (to stop rattles)
or just build a false floor cut a hole for the sub
make a box for underneath screw to the floor seal it up trim the top and fit the sub
easy if you know how:rasp: