Dried out RTV tubes

Thought I would ask a simple question about preserving RTV Gasket Maker. Just bought the third tube this year, 75% of the old tube dried out and wasted. I keep the cap on and the tube in the tool box.

Are there any tricks to keep this stuff fresh? Put it in a zip-lock bag? Put it in the refrigerator? I know it seems trivial, but I'm up to nearly $25 in a year for wasted RTV!