One of the only thing on the side of the tankers (or any non-self defense capable aircraft) is the fact that the MANPADs have a very, very short battery life. so if you change things up...its harder to predict where you will be. Change up which direction you will be landing and how your approach into the airfield is. Even if you do all of that, you are still a target and after a bit of time they understand the routine. Nothing can replace good solid manpower down below protecting your butt in the air.