I store my feeders in a deep freezer solely for snake food. I usually break them down into smaller ziploc freezer bags and only open the bags I need at feeding time. If you can vacuum seal them thats even better. I know you said you were using Rodent Pro but I'd highly recommend Big Cheese or Perfect Prey. I've used all three and the feeder quality and packaging at Big Cheese and Perfect Prey are far superior to Rodent Pro imo.
http://bigcheeserodents.com/frozen-feeder-rats/
http://www.perfectprey.com/frozen-rats/