here's a website for a company that specializes in these footwell enclosures for the boxster . . .
Monney Car Audio . . . but rockford fosgate products? yikes!
i bet you could purchase a carpeted enclosure from them if you don't live in CA.
the setup looks less intrusive than i expected . . . this solution seems better than the doors, in my opinion, if you can't squeeze a sub behind the seat.