@miranda A few tips from my experience making silicone prototype castings (for G-rated work purposes, but it's the same tech):
* You want platinum cure silicone, not tin cure. At a glance, it seems like you have the right stuff, but never hurts to be sure. Tin cure is what's used in bathroom caulk etc and releases acetic acid when curing so it smells like vinegar. Platinum cure is basically odorless.
* SLA printed molds contain chemically active sites on the surface from the resin that will inhibit curing, leaving your casting with a sticky uncured surface. I've had good experiences with https://www.smooth-on.com/products/inhibit-x/ to prevent cure inhibition but there are other options. You will want to use a release agent over this, the anti-inhibitor actually will make your part stick more
to the mold.
* FDM molds will have a slightly ribbed surface making your parts harder to clean and release unless you do a surface treatment to reduce the texturing.
* I've had the best results with injection molding: orient the part with the long axis in the horizontal plane, then use a syringe with a large blunt-tip needle (I used 14 gauge) to inject vacuum degassed, mixed silicone through a sprue at one side and have it fill the part linearly. Provide vent holes at the highest points in the part to allow air to escape.
Pouring resin into the mold can work, but I've found injecting under pressure does a better job of filling it especially if you are trying to encapsulate electronics etc rather than just make a solid hunk of rubber.