I started with pink (or blue) foam insulation board. The stuff I used was maybe 3/4in thick? Anyways, you need to layer it so you will have enough height for your tallest component inside the shell. In my case, this was the servo plugs going into the kkboard, and the vertical gyro on the kkboard. My two layers gave me more than enough height to clear the parts I needed to.
Next I glued the two small squares of foamboard together. The squares were just slightly bigger than my frameplate. I used a spray adhesive. Draw the outline of your frameplate on your block of foam. I used a bandsaw to cut the outline of the frameplate out of the block of foam. Then I covered one of my frameplates in masking tape to protect it from the coming fiberglassing. You now have your frameplate covered in maskingtape, and a piece of foam with the same outline as your frameplate. Use spray adhesive or thin double sided tape to secure your frameplate to your piece of foam that is shaped like the frameplate.
Now comes your creativity and some careful eyeballing as you can sand down your block of foam to give it the shape you want. DONT FORGET to have a mental map of the height of your electronics that will be under that completed shell. If you take off too much material, it's back to square one. I held my kkboard next to the foam and eyeballed it. Also remember that curves are stronger than corners, and that sharp corners will be hard to fiberglass. Sand your foam piece flush with the outer edge of your frameplate if it isnt already.
Next, once you have your shape, cover it in 2 layers of cling-wrap. Stretch it tight, and use tape to hold it tight over the foam on the underside of your frameplate. Then bust out the fiberglass cloth and resin. I use Z-poxy finishing resin. It odorless and less harsh than other fiberglass resin you might get at a bodyshop. Note, the Z-poxy resin does not harm the cling-wrap, but other resins may melt right thru it and destroy your foam piece.
I started off by covering the cling-wrap covered foam shape with a light coat of resin using my hands (with gloves on!). Then on goes the fiberglass cloth. I used 20oz cloth available at walmart, autozone and homedepot. It may not want to stay down, but once the resin gets tacky after about 45min, i will stick pretty good. I then did another layer of the same cloth at that point. And once that layer was tacky, I put down the outer layer of 3oz fiberglass cloth. It is fine threaded, and good for surface finish.
Once everything cured overnight, I poped out the foam piece from the cured fiberglass shell. I decided it wasent stiff enough, so I applied one more layer of 20oz fiberglass cloth on the inside of the shell and let it cure till the afternoon. Then I put the foam piece back into the fiberglass shell, and used it as a guideline to trim off excess fiberglass cloth around my edges with a good pair of scissors.
I then made relief cuts for servo wires exiting the shell, and drilled some holes to have the shell held on by zipties, and hit the whole thing with some krylon paint.
And there you have it, your very own "factory looking" fiberglass shell!