ORIGINAL: foodstick
There are a LOT of good how to videos on you tube. I experimented some with some clark foam. I had an old sailbord I cut up, The foam was great to work with, but after glassing and filling it..I still kept running into heat damage on the plug.. it was pretty disappointing, I would definitely start using wood from here on out...
One of the first big plugs I made was shaped out of regular white foam, then epoxy glassed, when I pulled the first canopy it collapsed in a little [:@],
What I did is take acetone and melt away the foam, then I filled the plug with plaster-of-Paris. Plug was solid as a rock then
good luck