Reference maquettes don't have to be made from Sculpey. Any materials that you've got in the studio or workshop can come in handy (which is a good excuse for being a lateral thinker and a packrat).
I constructed this very rough maquette for Arthur Denison's submersible using cardboard for the body profile and a clear plastic egg shape, which I filled with kit-bashed plastic model parts. The long gray pieces came from a model railroad supply store.
As you can see, I didn't follow the maquette closely at all, but it was really valuable for imagining Arthur Denison's submersible. I also referenced reconstructions of Bushnell's Turtle, a Revolutionary-era ancestor of submarines.
Combined with a kronosaur maquette that I had on hand, along with underwater photos of whales, I felt more sure of myself when I tackled a more difficult scene like this one, from Dinotopia: The World Beneath.