What scale are you working in? There is a 1/32 vac conversion out there somewhere. The tanks in it don't look symetrical, might not be as easy as I thought.
That looks like a job for modeling clay! The type that hardens. Then mold in two parts. As I have said before. Some of the custom made parts are a shame Not to duplicate them. Imagine the stockpile of parts that could be traded! I made molds of the wing tips I made for Merlin's Magic. Bill