I was an assistant gunner for an M60 crew during training in the Seabees. The tripod was so awkward; could never figure the best way to carry it or strap it on my back. I’ve wondered ever since why there wasn’t a fitted holder designed for that very purpose. (Then again, I was a Navy guy doing training under Marine supervision. Maybe my difficulty was their way of having a little fun?)
Maybe they've solved the issue, or maybe you're right about your Marine buddies.