Just finished making some "mother" or "master" molds for some RTV molds I wanted to reproduce. Used Smooth-On's 2 part pourable resin, with excellent results.
Basically, I formed an aluminum foil bowl or container around my original RTV molds, leaving just a little space around the edges of the molds. Then I just mixed up the resin and poured it in, starting by filling the cavities and then working out towards the edges. Took about 15 minutes to get fully cured and cooled, then just peeled the foil and popped out the RTV mold. What is left behind is a resin "box" with resin pours of the cavities molded into the bottom. I used a dremel to smooth up the edges of the box a bit.
Before pouring the RTV I sprayed a couple of coats of Smooth On's mold release in the resin "mother" mold. Once the RTV is cured, you just need to peel back a corner or side, and gently separate the RTV from the sides of the "mother", and peel it out. BAMMO...you have just reproduced your original mold.
This is a MUCH better way of reproducing molds (esp compared to pinning/gluing and pouring over multiple baits. Have made about 6 so far using the "mother" molds and there is NO variation mold to mold. Eliminates all the fumbling around with foil/tupperware types of mold boxes. Also cuts back on RTV waste because it is much easier to estimate the volume of the mold container (could also trim excess RTV from the original mold before the casting the "mother" to further decrease waste: such as trimming around a large curl tail). Have made them for 4" (zoom type) finesse worms, big flipping grubs, and 3" grubs so far...think there might be some issues on ribbed/zipper type baits (related to mold release).
In sort of a time crunch this week...packing to leave for Table Rock Sunday night...but will try to get some pics of this process/these items up ASAP. It works so well, I thought I needed to get the info out ASAP. It could really make buying commercial molds cost-effective. I have made LOTS and LOTS of molds, from all materials (except aluminum I guess) and this is by far the fastest and easiest method I have ever used for replicating your original.