Honestly I don't think any of the vehicles have any special "weak spots." Hit them anywhere with a weapon that can harm them and they will take damage.
I only play the PC version, so if I'm wrong fine, but that's my observation.
About the only thing that is different from that is if there is a gun visible (ie: a guy manning a turret or something) in which case you can save yourself some time by hitting the guy in the head, thus removing the danger of the turret without having to destroy the whole vehicle. Of course in the case of regular stationary turrets, a new enemy will hope right into it, so using a rocket to blow the thing up is a good idea too.