Rob: Yeah, established, popular sites are like camping on concrete.
Don't forget to wear yourself out during the day - you'll sleep soundly (whether on a plane, bus, or campsite).
Also, part of it is getting used to sleeping outside. When I've gone on multi-month trips, sometimes the first couple of days aren't super easy to fall asleep in, because my body hasn't adjusted to sleeping in the wilderness. Eventually, it gets into that rhythm. Of course, that doesn't help you if you're out for the weekend..... Hence, point #1.