It's interesting you say you'll make it hot in the shed as I was just wondering whether it would be better to make the environment warmer or cooler. The mixture will certainly start of with a lower viscosity if it's warmer but it will also set faster as well (a rule of thumb from chemistry is a reaction will go twice as fast for every 10 deg C warmer) which means there is less time for it to find a level everywhere. I can't help feeling you'd be better off working with it as cold as you can to give it time to spread out before it sets. It says it'll cure down to 8 deg C if you are willing to accept a reduction in mechanical strength. Might be worth an experiment, make up a small amount cold and pour it onto a piece of scrap, see how far it spreads then repeat with a warm batch / environment.