Answer: Mr. Sir ordered tents C and F over to help dig in X-Ray's hole
Stanley was assigned to D-tent. "D stands for diligence" according to Dr. Pendanski. In D-tent, Stanley lived with Rex, Ricky, Alan, Theodore, Jose and Hector. Or in the words of the boys: X-Ray, Zigzag, Squid, Armpit, Magnet and Zero.
In the book, Stanley was told by Dr. Pendanski that the counselors slept in F.