Yes, I use heat lamps to help cure it in cold and damp weather, works good. I steal the chickens heat lights when I need extra, lol... they are NOT amused!
When it's cold in the shop or garage I often make a tent around the area and use small space heaters to help. Old bed sheets, tarps or large pieces of cardboard work well. Make a tunnel to draw cool air into the heater.
With either body fillers or resins it's all about mixing in the catalyst at a rate best for the temps. It's the chemical reaction of the two that makes it set up and cure. With body filler, you'd have to mix it hotter than normal.
One thing that really helps with polyester resin is after the layup is done spray the area with a light coat of clear polyurethane. The thin coat makes an atmospheric barrier and cures the layup much quicker.
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