Do you have somebody with a drill or drill press?

Take a piece of foam, drill a hole for a 1/4" piece of dowel rod to be glued in the hole. You only need 3" sticking out of the foam to put in the drill chuck. Rough sand the shape on a SLOW__ SLOW speed. Safety. Final sand it. ..Then cut strips of ceral box into the strips and glue them on.

It will look great. I know it will work. Do it twice if you are picky.

You will never stop thinking of ways of scratch building once you do your first piece.

My PTB torpedos are a ton of work to make. Estes plastic nose cone--body tube-- a very pointed nose cone-- 1/8" thich balsa cut to the fins shapes-- spare props.
Boy , am I tired, it took 15 minutes to do 4 of them.