Forgot about the sandpaper thing, oops. Gotta try and think through the steps for painting props rather than Warhammer 40k tanks, haha. Another thing you wanna make sure is that the edges of the tape are smoothed down so the paint doesn't get up under the tape anyway. If you know how, and you have the means to do so, you can use any spots that the tape DOES pull up and turn them into wear/battle damage. Personally I use Citadel's Mithril Silver for it, but I imagine you can use practically in silver/steel colored paint for it(except maybe spray paints, but I've heard of people brushpainting with sprays, so I dont know).
@Ian: You mixed up the y and r in my name, friend. But because that actually kinda looks cool, I won't go off on you in a PM about it, haha.