Leave the LED lens exposed, its epoxy and already waterproof. only the leads and wires need to be protected. For your mold, try modelling clay (the kind that doesn't dry out, $1.00/ lb(+/_ been a while, cheap though) at Walmart. If you want to make many of the same shape, make a plaster of paris dummy of your finished 'puck', so you can just press it into the clay, pull it out, set your circuit, and fill. The clay is reusable, and uneffected by most resins, silcones, epoxies...