Can you specify the lenght of the lures?
For small , under 3" lures I also use RTV and foam from smooth-on(15lb 4X - expand) and never had a problem. I make the mold in a plastic pipe(there is a tutorial about this on TU) after that I do an evacuation hole on one side, then I place the mold on two large duck tapes but leaving the hole free for the foam to evacuate
Also as a tip, I use an X-Ray plastic for pouring the foam in the mold. I bend it and press it with my fingers, like that you will obtain a channel on the plastic. Mix the foam on it, plie the plastic, separe the mold opening, put the plied X-ray in it and let the foam go down. This way the foam won't get on the RTV opening, if it gets there gently wipe it with soft paper(napking)because it will expand and will open the mold, your lure will become fat.
Note: this is 1 piece molding