I've never done it. RK's look awesome and I have never heard or read of him saying anything about them leaking. What Cliff is talking about is whether or not this big ol hunk of aluminum can stand the change in temperature without warping. The case needs to be baked at 400 or so degrees to cure the powder. He also mentions pre-baking at 450. You would do this to heat the metal up so that any oil, grease or other impurities boil out of the metal. You would not want to trap this stuff under powder. Eventually, it will come out and there goes your adhesion. I believe that the problem may occur when the casting is heated, the metal has different thicknesses and so will heat at different rates. This will cause uneven thermal expansion of the aluminum. Then, the same thing will happen when cooling. Then you are going to do the same thing over again to cure the powder. Possibly a third time depending on what kind of powder you are using. The worry is that the machined surfaces of the cases will not maintain thier "trueness" and have a little warp in them somewhere.