Regarding Marines wearing pith helmets, I can't say for sure that I remember our PMIs or the guys that ran the range towers at Parris Island wearing them, but below is a picture of my buddy Cpl. Tim Wheeler wearing one as he was running "A" tower at the LeJeune range. This would have been around 1984. Tim was too short to go back on the second MED with us so he got assigned to the rifle range to finish out his enlistment. Not sure if he was a PMI but he did work the towers and he is clearly wearing a pith helmet in this photo. I told him I thought the pith helmets looked stupid, but he said they were required.
Weapons Plt Lima 3/8