+xAre you trying to work with the resin at this place, or do you want to have the final piece placed there? If you want to work with the uncured resin, you will not find any epoxy, that works well below 10° C. If my second guess is right, you could basically use every epoxy resin. The only problem might be the yellowing. But you can get uv resistant epoxys nowadays. Or uv protection additives. I think glasscast has good uv resistance, but I can be wrong there.
I will work with epoxy at 20 degrese when casting. When it will be fully cured it will be placed under roof but outside so it has to withstand winter and summer temperatures. So is GlassCast 50 Clear Epoxy Casting Resin for casting and GlassCast 3 Clear Epoxy Coating Resin for coat right decision?