Jeff, I had to make a rear cover for my modulus, I had a gig this weekend, and the alternative was cardboard and duct tape!
So I'm looking around my junk filled room looking for ANYTHING I could make a cover out of, to avoid looking all pUnK with cArDbOaRd and tApE on my bass. I ended up taking a regular matte black DVD cover, and cutting it into a control cover. It's thin, but isn't brittle, so I figured it would be easy to work with, and shouldn't break. Using scissors, I cut the front flat cover off, and cut off all of the outside framing to have a nice flat piece.
I took a regular piece of white paper, and taped it over the cavity to make a tracing of the hole. Once it is taped, I took a pencil, and ran it lightly (like shading) around the entire cavity. The outline is plenty visible, as it is much darker than the rest of the shading. I then took scissors, and cut it out, and laid it on the plastic. For a perfect non-slip of the paper, I'd reccomend using rubber cement to glue it on to the plastic, although I didn't have any, so I just laid it there with a hand on it at all times, being careful not to move it. I then took a sharpie, and traced around the paper template I made. After that was done, take the scissors, and as careful and straightly as possible, cut it out. I needed to do some fine fitting on mine, which was easily done with some sandpaper I had lying around. I wanted to do this anyhow, to clean up the scissor cut edges. Once I had a perfect fit, I laid it in it's spot, and carefully marked on the bass iteself the locations of th screw holes, so I would know where to mark them on the cover for drilling. The nice thing about this material is, it is thin enough that you don't really have to drill. I took a sharp knife, and started a hole with that, then laid it on the body to ensure correct location with the existing holes. Took 4 pickguard screws I had left from a previous project, and I'm done.
I was just doing this as a tempory fix, but I see no reason to change it now. While like I mentioned it is thinner than normal pg stock, it is pretty flexible, nice and easy to work with, and should be plenty strong for anything I would need it for.
Time invested: about an hour.
Cost: Zero, zilch, nada