Thanks for all the replies (on and off line) to my cowl bump questions.  

As most of you guessed, I won't be leaving the foam, so it won't have to be
good quality.  I'll take a look at the pink closed cell foam at Lowe's, and
also pick up a can of Great Stuff to see how it works.  The spray stuff may
be perfect for the bumps, and the sheets will probably be better for the
radiator scoop.  The problem I have with Styrofoam is that it doesn't sand
as well as I'd like.  As I recall, if you hit it with coarse paper, it just
pulls off in beads. I've got a whole sheet of the stuff up in the attic that
I was going to use for RC airplane wings, so maybe I'll hit it with some
sandpaper and see how it behaves.  

Rusty (did I mention I hate fiberglass)