I  notice that you use TB3 and you use rubber bands to fasten the backing on.  I use TB3 on my backed bows, and I use clamps, and works fine, but it's time consuming and takes a lot of clamps.  I clamp every 2 inches so I have 36 clamps at times.  I didn't think that TB3 would harden without oxygen, and with rubber bands I don't think it would get air in order to dry.  But if it will dry ok with rubber bands, then I'll switch.  BTW I live in eastern Ontario, Canada, and gets pretty cold here too.  Thanks for doing the build a long.