Okay, tried using UV resin with those molds from yesterday and while they turned out shit, I'm pretty sure it can be done in the end. UV resin is quite thick so it failed to reach all parts of the mold so I guess I have to open it and pour it more directly into cavities. Leaving it under direct sunlight for 30 minutes (mind you, they claim that it should cure after 5 minutes under sunlight and 2 minutes under UV lamp) made it mostly cured but breaking off one of supports made some resin pour out so I guess it requires more time to passively cure under normal light. I need to get better method of mounting parts and your suggestions of using hot glue sounds plausible (I hope I can just melt this glue with wire heated with a zipper, my gun is quite big and unhandy) and some method to get rid of air bubbles - probably some sort of shaking and pouring more slowly (which rise another problem of mentioned Fleximold cooling down while being poured).

Overall - fucked up on so many levels but also learned a bit so it's not complete time waste. And unless I figure out how to solve problem of Milliput copies in Blue Stuff molds being bigger than they should, this is my only potential method for making good copies of small elements.