I believe the
WAY they're kept is more important than
HOW LONG they're kept. The biggest problem would be freezer burn. It comes from the air making contact with the food. The same as any other meat you would keep in the freezer.
When you store them, get as much air out of the packaging as you can. Some people use those vacuum-sealers, others use two freezer bags with the air squeezed out. I use
GLAD Press-n-Seal, which then goes inside a freezer bag. I put each feeder in a separate "pouch", so I only take out what I need. If stored properly, they can last 6 months - one year.