RBaer: the mold turned out pretty good.. I'll post an after mold pic soon.. and your Pershing is looking sweet..! 
armournut: Acutally, making your own parts from rubber molds is pretty easy, a bit time comsuming( due to drying of the rubber molds and resin casts..) but pretty easy overall..
I used the Lego blocks as my mold box, easy to get, easy to reuse, cheap( stole em from my kid,,ssshhh! ) ... build the mold box big enough for the part, and have enough room for the rubber mold to extend beyond the part enough to keep the mold block stiff when removed. I then drilled a few small holes in the part and added a stiff wire to suspend the part by, coated the part and mold box with the release agent, poured in the liquid rubber molding compound, fill box up to part, and partialy up the side of the part.. set aside.. let dry... Once dry, using a sharp knife, cut in "keys" ( shapes in the mold half to keep halfs aligned when you make copies., I cut in pointed shapes like small pyramids) spray on more mold release agent.. Fill box with more rubber mold agent. Let dry... remove Lego blocks, seperate mold halfs.. Once seperated, cut in with a sharp knife, a pour hole, and a vent hole, these should be two seperate holes in the top most part of the original part as it sits in the mold.. Air needs to escape when you pour in the resin casting agent. Coat with mold release agent, put mold halfs together aligning the keys( I use rubber bands and popsicle sticks to hold together).. Pour in resin, untill resin comes out vent hole.. Set aside.. till dry n hard. seperate.. ,, cut off excess resin.. and tada!! your done..
If your order a Resin casting starter kit from Micro Mark ( about $88.00 ) it comes with all you need, plus.... and instructions.. I'll post pics of my mold later..