Years ago I ordered gut in bulk from Bow Brand. I spoke with the sales rep and asked the same question. She said to simply store it in a ziplock bag in an area with a constant cool temperature (e.g., basement) away from direct sunlight.
If you do that, it can last for years.
"Nobody beats Vitas Gerulaitis 17 times in a row" -- Vitas Gerulaitis, after beating Jimmy Connors on his 17th try.