A very common Mod. is the warm air intake, many guys use insulated pipe and run it from the first Cat. I myself just ran a shop vac hose to my exhaust manifold (i'm cheap
) I had considered a solar powered fan to move air through the car while parked, but never had the time or money to consider it seriously. The thought was to set a small solar panel in the rear deck along w/ some pass through comp fans to the trunk, then hosing to push air out some holes cut through the brake light housing (sounds crazy, but would make sense if i drew it out or showed you what i was talking about)