Haven't used a propane heater to heat a boat building shop, but they are cheap to buy and operate. And they really heat. We just finished an archaeological excavation here in northern Minnesota (something else we do when we are not building boats) and we used a home-built 12' x24' shelter out of 6 mil poly with a "blue tarp" roof. This was set up over partially frozen ground which we had shoveled the snow off. We used a propane convection heater which we bought at Sportsman's Guide for $79. At temperatures in the teens outside, we were working in t-shirts after about 20 minutes. A 20 pound of propane lasted about a day and a half under these conditions. We had plenty of air leaks, so fumes were not a concern. Not sure how this works with epoxy, but it will definitely give lots of cheap heat.

FWIW

Grant