In reply to rockafunked:
We use camping dolomiti and highly recommend, not too formal and good facilities all included in the price (although the WiFi is pretty poor). We have never booked, but that said have been in July or September rather than August and by early August the site is getting appreciably busier.
Dolomiti, Rocchetta and Cortina are literally adjacent to each other along the river so if no space at one only a few minutes walk to check out them all out. I suspect that if you turn up with a small tent and no car they will happily let you find a spot to pitch regardless of how busy they are.