Following on from my previous thread in "Pattern and plugmaking" http://www.talkcomposites.com/623/Pattern-Making-and-CAD,-need-advice 

in which you can see the design and pattern making of this spoiler



My plug is now nearly ready



I'm now thinking about how to make the mould, i'm considering making a 2 part split mould as illustrated cross section below, i haven't done this before so please add your comments on how you think it would work out or how i can do it better.

what would be the best material to use for the barriers?

whoa! i have the EXACT same issue! i have a foha spoiler for my 87 bmw 325 that is long out of production. i am going to mold it on the car.
also will make the bottom on the car too.then bond the bottom to the spoiler and possibly use windshield urethane to attach to the decklid.
thinking of filling it with lightweight foam as well.

good luck on your spoiler !!

CarbonFiberCreations