[Lew Silverman]

If you install a roll-bar or -cage, and if you're running any stock class "M" or above you're required to do so, you can remove the rear seat. You have to carpet the area where the seat was installed to finish the installation.

As David mentioned, modifying the inner wheel-wells with a "mini-tub" is prohibited, although you may be able to gently "massage" certain areas to get enough clearance.