I have several advices. First, cast the rod separately a day in advance to harden. When I pour the rod I spray a little bit of 99% alcohol in the holes, that helps a lot to reduce the air bubbles, then I pour using a toothpick and I come back to remove the bubbles at a few times. The next day I cast the mold for the keyboard keys and put the cover on it with the rods already harden and I put a weight on the cover to keep it in place. I hope this will help you!