I'd probably go with the most dense I can get. My prototype has taught me a lot already. The ribs are impossible to smooth out and they lose definition when cleaning up the mold. I will probably just go with a smooth shoulder on the next one. It should make release a lot easier too. I used titebond iii to laminate the MDF one coat thinned to soak in, then a second coat straight out of the bottle. Hopefully the wood glue doesn't separate like the laminating epoxy. Sanding it after it is sealed is much harder and the sealer soaks in really well. And folded sandpaper in tight spots does a number on your fingernails. They are really short and hurting now.