Smooth? Easy, on top of the foam 2-3 coats of resin, then bondo, then sand and shape and smooth with files, rasps, and 60-80 grit sandpaper, once its uniform do a coat or two of spot filler/glazing putty and sand that smooth with 200 grit wet-dry sand paper, I prefer to sand wet at this stage then prime, wet sand any spots and then do a 2-3 coats of paint for the mold as it fills in most little gaps after that and ta da, ready to be molded. It's gonna be cast in Smooth on black two part plastic with aluminum powder brushed into the mold so if it scratches or rubs any paint off it still looks metal underneath instead of white. I also decided to opt for Metal tapping screws instead of rivets thinking, if I need to do field repairs a screw is a lot easier than a rivet. Blam.