What "SecondHALONICK" said about this achievement is completely right.
I just want to add an easy method for you if you struggle doing this the first time because it can be really annoying that the target is constantly moving around.
Just wait for the convoy near the road and as soon as they pass through, detonate the C4 you placed on the road or shoot at it with your rocket launchers (e.g. RPG). This is pretty much the easiest way to do this since the convoy will always stay on this route, they mostly drive around in a small circle. If you miss them once, don't worry - they will be here again in just a few minutes.
By the way, you can completely ignore the machine gun Jeeps that protect the truck. As soon as you destroy the truck (which carries the weapons) you got the mission done and the achievement is going to be yours.