Wow, haha. I'll try that as well. Thanks.Ooooh yeah, that one. What I did was first make sure I was ahead of where they would be(interrogated soldiers to be sure) then parked a car in the middle of the road. In the absence of a car, I'm pretty sure the horse would also work haha.
Then, from the top of a hill, I sniped the driver. It took two shots to do that because the first shot only broke the window, so you probably have time to switch out to non-lethal ammo if you are going for a complete no-kill run. Once the driver is dead/unconscious the car that's packing the Skulls just won't move at all, and the tanks don't move either until you aggro them.
At that point I lamed the fuck out of the game by riding my horse back to the nearest city just to get a checkpoint in case I messed things up, because I'm a huge, shameless cheeser and had died too many times there. After that I doubled back, got a supply of a rocket launcher and shot both tanks. Then, before approaching the truck, I left my horse by the middle of the road as my escape route.
Then once I approached the car and triggered the Skulls, I sneaked behind them to fulton the tank and ran like a coward to my getaway horse I had prepared earlier. After that I just ran like a lunatic back to the helicopter.