I have no experience with silicone. What part will be the tricky part?
One thing that I can see that can be tricky is the gap between the toes of the shoes and the fluke. Even with cloth tails, that is an issue. As the fabric works, some slack gets into that area and starts flapping about. To deal with the issue, I made this fairing out of neoprene:
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The picture I posted above (post #55) of the complete tail has the fairing in place. Its attached with Velcro patches, each located where the black Sharpie marks are on the neoprene, and stretched tight. It does a good job supporting the fabric, and stood up to a test swim. But, half way through making it, it occurred to me that I could have made the fairing larger, allowing me to fit it round the entire shoe. That would eliminate the Velcro on the shoe, and cover all the shoe straps and shoe-to-monofin attachment plate as well. More neoprene is on order.