A ways back, I found some pourable urethane in black that was intended for under-hood use. It was a two-part mixture. Came in quarts and pints.

My thought was to make something out of blue builders foam, and then brush the stuff on in a few coats. Then, eat the foam away with gasoline (this works on styrofoam anyway).

Can't find the link, but I think it was McMaster-Carr catalog.

Luck to you,

Kevin