I always thought they only did things like this in rockets.

http://www.jgtc.net/race/gallery/gall2004/044gallery_ph/044q056.jpg

haven't seen the other JGTC drivers doing this.

You sit in the hot car, bouncing around, drinking water constantly to keep hydrated, and only sweating half of it out, for hours on end. Its not like they have time to stop, now do they? It's my understanding that most motorsport does this, save for the ones where they race for about five, and hang out for a while before racing again (some touring, drag....).