I'll be milling some moulds out of epoxy. I would love to try the s120 sealer but it's just too expensive to ship to the states. Does anyone know of something similar I can get here? Also I'm curious what type of epoxy/filler will work nicely for this? I will probably be building up a layer of epoxy over pre milled mdf leaving a few mm thickness for epoxy and milling final shape into that. Already tried bondo and that works, but I think epoxy/filler will work nicer and be tougher, just not sure what to use. Another guy mentioned coating the mould in Teflon tape which i might consider, but I want to see what is available to use that is similar to s120. 

Ok, I think I found something. Chemlease Sealer 15 EZ. Seems to be a very similar product to s120. Can be applied by spraying or wiping, designed to give a mold a nice smooth base surface, fills microscopic porosity, etc.