Silly, simple, drew up in 3 minutes 20mm mounts. They get the idea across from across the pond. Use a 1/16" rod for a gun barrel. Or don't. Its your boat.
Files are provided for single up to x5 mountings. You can manipulate these easily enough to make whatever you need, either digitally or with snip and knife physically.
Simple US 20mm Mounts 1.0
20mm Mounts for USN BBs and others
