To add-on to the above solution: don't die. At all. Even on normal, you won't reach any checkpoints going over the mountains, so be especially careful when securing the LZ; otherwise, you'll have to start over with the POWs at the convoy.
Other than that, the mountains are the way to go. You'll encounter two enemy Spec Ops teams at the most, and they're a piece of cake to take down when you've got eight men. If you're especially cautious, send the POWs away when you anticipate the Spec Ops teams, but they tend to be very sneaky and and I haven't yet lost a teammate to them, so don't sweat it.