If you mix body filler hot enough, it will cure in 10C temperatures, but Resin takes too long even hot to set well in that temp (unless it's part of a Rondo mix). If it's 10F you're kind of boned..
Smoothcast is a plastic pour, it won't be as strong as fiberglass, but it can be pretty good. You may want to look into water based resins which can be mixed inside a house.
You can also try mixing and applying your body filler and resin and then putting the armor under a box with a blow dryer or other heating device and CAREFULLY watching them to make sure they don't catch on fire. This is the "hotbox" method a lot of people use with some success.
The hotbox is not that dangerous, a decent hair dryer and really those giant buckets you can get at hardware stores for like 5$ work well.
But if you don't wish to go that route, I understand. Smoothcast will be a LOT more expensive though. If you pour it thick enough it'll be strong enough for mold casting, but it might cost you more than trying a hotbox. It's all about what money you have and how much effort you wish to put forth. You could even get a space heater and put it in a shed with the piece, or a detached garage. Just some ideas!
Should I worry about getting bugs or viruses from using the downloaded pep designer?
I've been lookin for almost two hours but I can't find a good jorge helmet pep file that isn't Brandon Mclain or whoever, it won't let me download it. any links for the helmet would b great
How do you size the armor so it fits you?