mounting my sub: where to mount?

i want to mount a subwoofer in my trunk. i have everything all set but i just need to mount it. i would prefer to sandwich a board between the carpeting and frame of the car and mount it to that but i wanted opinions on where i could mount it.

any ideas?

rear quarter panel? how big of a sub are we talkin here

One option is to pull the spare tire and build/fiberglass a box into the trunk well.

or buy a premade box and use self tapping screws and l-brackets to secure it.