[3-Wheeler]

I noticed that Bicycle Bob is advocating making the skirt from about five layers of fiberglass cloth, and this would work fine....

But there is another way that I have successfully made various shapes over the years.

Make the entire shape of your skirt with polystyrene foam that is bought for home insulation.

As you mentioned, cut/carve/shape and so on to get the shape you are after. When doing this, try to keep the minimum thickness of the foam at least 1/4 inch thick in the thinnest spots, and up to 1 inch thick where you can.

Now when you have the shape exactly as you like it, you can apply the cloth with your choice of resin, but if you use Polyester, then you must coat the foam with something like Latex primer paint before adding the Polyester resin.

For a part this small, I would pay the extra and use West System Epoxy resin, which does not eat the foam in the process, so no painting is necessary before adding the resin.

Add one layer of 6 ounce glass to the outside and inside for strength. No need to add more layers, as this will be plenty strong.

Add wood blocks inside the foam where the skirt attaches to the car, and add several more small patches of glass in these areas for support.

Almost forgot... Making a foam/fiberglass composite will result in lower weight of the overall panel, since there are only two layers of glass, instead of multiple layers when making a fiberglass model (at least five for strength) from a plug (male or female), depending on what surface you want the smooth finish. In the case of the polystyrene filler, the extra thickness of the filler adds hardly any weight, as the density of the foam is low compared to the weight of the fiberglass and resin.

Also keep in mind when doubling the thickness of a panel, the buckling strength goes up four times for this thickness increase, with only a small increase in weight. Formula race cars use this same construction technique, except they substitute aluminum honeycomb for the foam core, and carbon fiber for the fiberglass cloth.

Jim.