I've done a bunch of stick for members here with duracoat with airbrush a d spray gun. Prep is the key. Degrease and when your sure you have it clean degrease it again. Duracoat will not stick to any remaining oil. Spray the trustrip on liberally and wipe with clean cloth/paper towels. My suggestion for the barrel would be to tape the whole thing with painter's tape then press along the edges of the flutes hard. Follow the edge with a exacto/hobby knife and cut the flutes out. Press the edges back down to ensure a good seal...duracoat is thin and can creep under the edges.
If doing a polymer stock and worried you might not get it clean enough and have chipping/flaking issues you can get adhesion promoter for plastics at any auto parts store. Spray on let it tack up and apply duracoat. I've used dupli-color here and there on well used stocks when residual oils/cleaners could be an issue.
Good luck and if you need some help shoot me a PM.
