I'll agree with the XV and US-Tool-Works products as they've done some interesting studies... shown in their videos. I like the SFC that become welded across the floor pan, but with certain club "rules", that type is not allowed (too bad!).

Mopar Mitch "Road racers and autocrossers go in deeper and come out harder!"... and rain never stops us from having fun with our cars... in fact, it makes us better drivers! Check out MOPAR ACTION MAGAZINE, August 2006 issue for feature article and specs on my autocross T/A!