Well, if it's humid out then there's not really much you can do except tucking in an airtight container in the dark and hope for the best. Isomalt sugar is more resistant to humidity, however it doesn't carmelize the same way the sugar does, and I'm not really sure if it would be appropriate for peanut brittle.
Location: I live in the Heartland of the United States - Western Kentucky
We live in a humid area and have difficulty with storing things that have a tendency to take on moisture. As a result Buck says I've become the "queen" of Tupperware. So far storing those items in Tupperware seems to have solved our dilemma.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!