No you can not camp on a vacant lot in Cambria. You would need to purchase water and sewer rights and have them transferred on to your vacant lot. You would be allowed to have a trailer on the property while you were building your home, but the county has limitations on how long you can occupy the trailer.
That is a very common question, the answer is no, you cannot camp on it. You could buy an active water meter and move it to the lot as long as the lot meets certain specifications. You can find answers to many of your questions on the Cambria CSD website. It would be in your best interest to talk to a Realtor IN CAMBRIA who is familiar with the water situation (ie. special project area's, transfer rules etc). Good luck.