I assume you have an airbrush because that's a great finish on yours.

I know a lot of guys swear by the hairspray technique, but I don't like the idea of putting on something that may or may not adhere well to a model, especially one that moves.

My approach is the same as before that method came out a few years ago. I give the entire (clean) tank a good coat of Future. This completely seals the original coat and makes it a tough finish. Think about it, it's original purpose is to be mopped on floors to protect them. In modeling, it's used to seal, adhere and fix canopies, smooth finishes for decals, etc. If you haven't done it before, airbrush it in light coats at bout 10-12 PSI.

Once that sets, hand or air brush white or off white paint for the whitewash. As soon as it starts to dry, use another brush (clean and wet) and paper towel (also wet) to rub off where you want. It's a very effective technique, you can redo if you remove too much, remove more, remove it all without disturbing the underlying finish. If it's intimidating at first, test it out on the underside of the hull or scrap plastic.

Once you rub away the traffic patterns, where it would be splashed or rained off and like the way it is, clear coat it and it's done. If you plan on weathering on top of it, coat it with another coat of Future to seal, making even tougher and giving you a great base for washes, oils, whatever.