I am in Texas and I was storing my Monokote in the garage. It got hot enough that the adhesive must have activated because I could not peel the backing off without the adhesive coming off with it. Had to dispose of several rolls that were affected in this manner.
Since then I store it in the house and have used stuff that is more than 5 years old without problems.
I figure that if you can peel the backing off of it normally it will work just fine.