Thanks for the tips jo
The minimum wall on these parts is 2mm on the frame model and 3mm on the slide section. Going to buy the prints through shapeways (as long as they don't figure out they're for a replica gun lol, I've uploaded them separately as an lcd display frame and a speaker housing, fingers crossed)
Their black strong flexible material is a nylon plastic. Expecting them to be textured as my badges are which I may leave as is but if not it'll be either lots of careful sanding or if its too much hassle they now offer white strong flexible polished so I may try that and if it looks good I can just paint the parts after they arrive. Do you reckon these are thick enough to avoid too much warping?