[Bicycle Bob]

BTW, webmasters, Styrospray is something I found by clicking an ad on this site, the first time I've responded to a web advert in years. This site is tops in quality flack, too!

Another option for styrofoam and polyester is to use a barrier coat of SB-112 epoxy from System Three. It won't melt the foam, yet the esters stick to it. It is also very handy for any bodywork. It will seal in rust pits, and take bondo on top.

I'd say that Vinylester is roughly the equivalent of decent, lightly baked epoxy. Generally, though, the epoxy is tougher, which is often what matters most. That works against it if you are doing any shaping, sanding, or polishing, though. And when refining a shape, it is very handy to be able to mix up a bit of quick-setting ester. It even works a bit better for green trimming, which is a great time saver. And, of course, you can mix in Bondo (lightweight, for ecomodders :-)

If you have a CAD setup, you might be able to print out shapes for templates that a hot wire can follow, complete with station numbers for synchronization of each end of the wire. Given the accuracy of hot-wire, etc, you'll have some filling to do. It is a great advantage to be sanding only one hardness composing a surface.
For a quick build, do the 1st coat of filler with a notched trowel. That gives much less sanding to establish the contour, and the grooves are then easy to fill. Random Orbit sanders are nice, but for this stuff, longboards are your friend to create fair surfaces. Just glue coarse sandpaper on to strips of 1/4" (6mm) plywood or something similar.
Have a look at Fartstone glass foam blocks, too. The wear into any contour, cut fast, and finish smooth. They get their name from the hydrogen sulphide used to foam the glass, but you have nose protection anyway, na?