Well, the wood from the side of the fuse extends enough to cover the sides, then you just need to fill the top and bottom and front like say on a sportster, and it is a cowel. Another option is to put a piece of foam on the front, sand it to the shape you want, glass it and melt the foam with gas, or use the foam for a plug for a mold.

You could use just about anything that fits. I just left the sides long like they come in the kit, and left the top and bottom open. It looked pretty good.