This post is old and you might have had your bow already finished, however I will still add my experiences with Urac 185 because someone else may read it.

I have used Urac 185 on several longbow projects and never used a heat box. It's in the winter when I usually embark on archery projects when the temperatures are 50 degrees outside. Normally I glue it all up and let it sit for a day or two outside in the garage or at my friend's barn. No heat. Works just fine without all the heat box stuff.