Well personally, I have not ventured into a project like my own kit, I have reinforced (and repaired) my current kit and made few adjustments to last front end. But that is the extent of my fiberglass on kits goes.
I have never used foam, just chicken wire, fleece and MDF but I have read a little about it and I will try and shot you some Ideas. And all I say is what I have heard, I have no first hand on foam. There is green floral foam at wal-mart and so on, but NOT the sandy kind that falls apart when you touch it. This Foam is suppose to be easier to work with then 2 parts expanding foam, and Generally cheaper. You can find some of the foam here, and from what i have heard it is at a cheaper price then most.
Link As for the green flower foam from wally world. After you make your mold and all the resin and glass is layed and set if you are unable to remove the foam from the glass then you can pour acetone on it and the foam will dissolve (it is referred to as "sacrafical" since you can kill it) But I am unaware of the sizes that this foam comes in and it may pose a problem on getting it to all flow. You could always make say left and right of kit (since generally they are busier then middle) outta foam and then use another method for the middle.
Getting a visual of all this makes it seems like it would be damn near impossible to pull it off accordinly. You would have to make mold, inset your air holes (holes in kit) and not resin those parts and the girll would be tricky. Not to mention getting it prefectlly ummm.....that world that means even on both sides (can't think) would be hard as hell. There are a couple good books at barnes & noble and so on about glassing. I would highly suggest you go pick one or two of them up and school yourself on the matter. This would be serious undertaking and intial cost of glass is cheap, but it nickle and dimes its way in ya bank.
