Hello,
This is how I make my molds using Bondo. First get a aluminum pan that has tall sides and spray it down with WD40. Mix the bondo and pour the pan half full. Spay the bait and press half way into the bondo. Take a pencil and make 4 small indentions at the corners. Let it have time to setup. Leave the bait in the set bondo and spray all of it with WD40 and then pour the top layer. Once the top layer has time to setup simply remove and use a dremel tool to cut a fill spout. The indentions that was made with the pencil will allow the two halves to go together tightly everytime. The trick to bondo is the WD40 because it will not stick to anything that has been sprayed. This is the simplest way that I have found to make a mold.