Hopefully, there'd be a variety of possibilities. Even a shoulder rig wearable under a field jacket or ECWCS parka.
A nice little zippered or velcro-seamed carry bag, like the *fagbags* some US SF advisors in El Salvador used for Mac 10s or H&K SP89s, would be a nice touch, too. Keeps the dust out while in the sandbox.
The barrel bag for an M60 MG worked pretty well for an M3 greasegun or Swedish K.
You know, I'm pleasantly surprised by how the USMC of all branches have become the innovators.