Alumilite High Strength 3 can be used as a casting if you use a hard mold and it's rated to have a very high tear strength, I usually go straight for the scissors when I need to cut it as I know for a fact that it will not tear easily - it's meant to stretch and flex but not tear.
I normally use Plat 25 (food grade silicone) more as I make custom candy molds so I know it's rated for freezing temperatures such as for ice cubes but I'm fairly certain the High Strength 3 can also handle the cold as I've stored it in an area that gets freezing cold. Both silicones can handle up to 395 degrees heat but you mentioned weather conditions so I would suggest the High Strength 3 for longer use in those conditions and the higher tear strength it is rated for.
As for what silicone that oven glove is made of, that I am not sure of as I don't own one so I can only suggest trying the High Strength 3 from what I've done with it myself. It may be listed as a "mold material" but there is no reason why it cannot be used as a casting material too from what I've used it for.