current temps are in the 30's during the day

You will need a warmer temperature for the resin to kick, so I would suggest using a bucket of hot water and put the end of the mystery in a plastic bag in case of seepage. Then I would do a small batch so you don't risk overheating and cracking. For a larger fill I would displace a small batch of resin by imbedding a shaped piece of wood in the end, lighter and less chance of resin fracturing.
Reg