Cart bodies -- whether they're fun, customized golf cart bodies or racing go-kart bodies -- are essentially like any other fiberglass part. You can create your own cart body using standard fiberglass molding techniques. Whether it's for turning a golf cart into a miniature Shelby Mustang or for circling the racetrack a little faster, the process is the same.
Acquire a plug. The plug is a mold used to create a fiberglass body. It is the inverse shape of the cart body. You can find specialty companies that sell them, though you may need to cast one from an existing body that you like. If you decide to cast your own, the process is exactly the same as creating a fiberglass part from a mold, only you will use it as a mold instead of a finished part.
Thoroughly coat the plug with mold release. Wipe the mold release on in a circular motion, just like you would apply wax to a car. Mold release is a wax-like substance that keeps liquid fiberglass resin from sticking to the mold. Once the fiberglass dries, the mold release will allow you to remove the part without damaging the part or the plug. Apply at least three coats and work in a well-lit space so you can see the coverage.
Spray a coat of gel coat into the mold. Gel coat is essentially liquid polyester fiberglass resin with color emulsified in it. If you do not have a sprayer, you can paint on a layer. You can also substitute regular fiberglass resin for gel coat, but it is not as scratch-resistant and does not contain pigment.
Spread the fiberglass cloth inside the mold the way you would lay pie dough over a pie pan. Then gently spread it into the contours of the mold. It won't stick; just position the cloth, preparing it for resin.
Mix a two-part polyester fiberglass resin. The resin is the liquid component in fiberglass, which is mixed with the second part -- a chemical hardener -- that begins activating and drying the resin as soon as the two are mixed. Pour a mound of the mixed, liquid resin in the bottom of the mold, then spread it out with a brush. Work briskly, as your working time is limited. Working from the bottom-center of the mold, continue to pour mounds of liquid resin onto an unsaturated cloth and working into the cloth evenly. Work in a concentric circle, from the center of the mold to the edges.
Repeat the process with one or more additional layers of fiberglass. For reinforcement, use heavier fiberglass batting for the second layer. Otherwise, employing the same techniques. Or, if you prefer, use two additional coats each with one layer of fiberglass cloth.
Allow the fiberglass to thoroughly dry, or for at least 24 hours. Remove the cart body from the mold.