You are looking for a liquid rubber rather than a gum rubber. Liquid silicone rubber (LSR) molding has become a very common process. I am sure other liquid rubbers exist but I am not very familiar with them.

Your part seems very similar to a condom but with two open ends. Is it now made by latex dipping?

So, something like this https://www.homedepot.com/p/Plasti-Dip-14-5-oz-Bla... is available at Home Depot

Other choices
https://www.atlantexmfg.com/pyrotex-end-dip/
http://siliconesolutions.com/high-performance-coat...

TTFN (ta ta for now)
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Right now I'm prototyping with Latex finger cots, which is the closest thing I could find. Since this is for use in a medical device, Latex material cannot be used.

The final product will probably be injection molded or dip molded. LSR could be a good option but for my application I think TPE/TPU material will work better.

As an intermediate solution, perhaps some other liquid rubber coating, as you suggested may work to make parts to correct dimensions.

Thanks

I think Compositepro (Chemical) has it right. You want to look for a 2-component liquid silicone molding rubber. A two-component material will give you a chemical cure, whereas 1-part materials usually require the evaporation of moisture; which is not going to happen in a mold.