i did this: I left the bolt that sticks up through there in the well in place, and made a thick fibreglass mould to sit in it. There is a hole cut out for the bolt to come through.
Next i made an mdf floor (cut round boot carpet) and cut a 12" hole in the correct place for the sub. I then fibreglassed the fibreglass mould to the mdf, and also bolted it to the mdf.
Then i put it in place, put a washer + nut over the spare wheel bolt to keep it all in place. dropped the sub in (its not in the center of the spare wheel hole as the bolt is in the way, its left of it and further back) which was a perfect fit. because of it not being the center of the wheel well, it looks central in the boot.
thats just the sub bit, i then made a false floor on top so i had a cavity for all the wiring and amps, carpeted it and you cant really tell its there looking at it.
