I used kraft paper scraps from my wife's bindery (she's a book binder) to trace the curves for cutting onto the styrofoam. The foam was glued to the wood with Titebond II.
The empty sections will have the shore outlet connection and a soffit vent, so I haven't decided when to put the insulation in those spots. I suspect it will be easier to cut out the wood and then carve the insulation around any holes, but we'll see.