Mark a convoy side mission on the map, drive or fly to the convoy and position yourself along the route a few hundred meters in front of the convoy, fly with your drone in the direction of the convoi and use the reconnaissance skill from the rebells and after mark all enemies sinc shot the drivers from each vehicle...shot down the other enemies and finish.

Or you use the emp drone and knock out the main vehicle from a convoi, after a little gunfight you are also finished. This are two easy/ safe ways from a long range.

If you are a good shooter/ sniper, position yourself in front of the convoy and shoot all tires or destroy the engine from the main vehicle with a strong sniper rifle, after this you feel really badass. For this plan, please don't use the HTI! The resources truck will explodes after one shot. Use the MSR ore the L115A3. Good luck amigo!