I have had good luck with medium starfish, I dry them out on a window screen
where air can circulate all around them for a couple of weeks. The smell is
usually gone by then. Make sure the screen is tight and doesn't sag, or when
dry the starfish will not lay flat.
If they are a smooth-arm starfish, I usually flip them over and put hot glue
down the fissures of the arms, which makes them a lot stronger.
A light coat of varnish (not the glossy kind) can be used to seal them, and I
have never noticed an odor after this.

Scott
Florida