Madbadger, your tank looks great. I would suggest you spray your tank with Dullcoat before you start weathering. This will seal and protect your original paint job. Weather with washes of thinnned acrylic paint, and dust up the tank with your airbrush. If you goof up the weathering, you can then use Windex to strip the weathering off and do it again. The coat of dullcoat will protect your original paint job from the stripping action of windex.

Also if you use chalk powders, be warned that when you spray this with Dullcoat you loose at least half of the intensity of the powders on the tank.