Bill, for a 30-hour race most Elite teams won't sleep or rest at all. In our case, for races of 36 hours or less, we do not sleep. For longer races we start considering taking a couple short naps, but for 30-hr is not worth it.
But as far as sleep, obviously the more comfortable you are the better. I can tell you from many years of experience doing the Coast to Coast AR during Memorial Day Weekend, that trying to sleep outside without a tent sucks because the mosquitoes and other bugs are just insane. So if you are planning on napping at all, I would definitely suggest you put up a tent.