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?