I built a couple s&g in a plastic wrap tent very much like what et shows, using radiator heaters, and cured epoxy all winter in eastern NC. I agree though you want to keep your epoxy warm so it doesn't become too viscous and unmanageable. For local cure jobs, you can tent the kayak itself, heat lamps, radiators... Just don't setup a fire hazard. And beware any heater like kerosene that would put an oily residue into the air to settle on surfaces.