It is strange that there is a barber tent among the relatively small number of tents actually set up in the M*A*S*H exterior set at the Fox ranch. But there is no mistake that such a tent exists and is clearly marked. It is seldom used or referenced in the plot of any episode and interior scenes of the tent are extremely rare. Who exactly is the camp barber?
The barber tent is located next to the mess tent. The slope leading up to the Upper Chopper Pad runs just beside it. It is clearly marked with a sign saying "Barber Tent" and a striped red and white bar. In any camp, the personnel are going to need to have their hair cut. But on the 4077th, we often see the camp personnel having their hair cut while sitting outdoors. There are many scenes featuring Nurse Kellye cutting the hair of various people, for example.
Just about the only scene we have inside the barber tent comes from "Lt. Radar O'Reilly" (Season 5) where we see Col. Potter inside having his hair cut by Klinger. That may be the clue. Klinger seems to have his own tent where he is often seen working on his Klinger Collection, complete with mannequins and sewing machine. He even has a salon style hair dryer. But Klinger is only a corporal. How does he get his own tent? Perhaps Klinger camps out in the barber tent?
In Season 4 "Hey, Doc" Frank's poor tank driving skills actually demolishes a tent which Margaret says is the girl's shower tent. She even rushes in to drag several nurses out wrapped in towels before the tank smashes it. But from the position of the tent, it is clearly the barber tent which is being crushed.