might have to create some baffles for that. By a stretchy material that can soak up resin (fleece) was mentioned above, some people don't like the mat to be so thick, other people have used like panty hose, basically anything stretchy that can soak up resin. pull and stretch the design you want with that and stiff materials like wood or something to hold the fleece. Staple it down when it is looking good, try to cut the fleece as little as possible while keeping the shape as smooth as possible. Then just resin up the fleece add fiberglass mat in strips and coat that down with resin/hardner mixture. and repeat untill you have a lot of layers since you're making substage with it. need multi layers for strength. let dry, apply some bondo or some kind of buffering material and sand it down to get a smooth nice surface, then paint. Or forgo all that and just wrap it in some felt or carpet or vinyl or something.