If you haven't vacuumed the rubber, it's generally not a good idea to pressure cast. The small air bubbles in the rubber will collapes and leave bumps on the surface of your part. Looking at your mold layout you're on the right track for that style of mold. Try using talcum (baby)powder in the mold, it will help the resin to flow better over the rubber. You may also want bigger runners for the resin to flow faster as well.