Keep in mind what one person doesn't call a scratch another will -- for that reason I'll never use a magnetic bag on the 250 (when I upgrade, I do plan on getting a ring-lock on like the OP had).
If you do get one, I'd recommend looking into tankslapper film -- Essentially it is the same/similar to what is used to clearbra a car, and given the cheap price if it did scratch the film you could just remove and replace it:
TheTankSlapper.biz - The Product
If you do get one, I'd recommend looking into tankslapper film -- Essentially it is the same/similar to what is used to clearbra a car, and given the cheap price if it did scratch the film you could just remove and replace it:
TheTankSlapper.biz - The Product