I dunno if I'd use a clearcoat.... anything you spray over your weathering will probably darken and possibly dull your weathering. Especially if you are using metallic paints. Anyone ever clearcoat something metallic? I'm not saying it will ruin your hard work, but it may no longer appear exactly the way you had so painstakingly worked towards.
Even if you used a semi gloss or flat in very light coats you would still be creating a uniform surface over the prop that clearly has different textures and finishes to each component. If its for display most of the time just weather it till your happy with the look and enjoy.
EDIT:
Yeah, and AWESOME blaster dude... its the nicest I've ever seen.