sanding corners like that can be a bear, so what I have done with that sort of thing is smooth on a piece of aluminum foil or anything that the epoxy putty should come off of, to the gun and shape it in place and once it has firmed up a bit, take it off and then do the shaping and sanding. once it's worked out, then glue it in place. usually much easier in the long run.
nice job BTW!
Ok thanks for the tip