I agree with both using a good stabilizer and installing a manual fuel shutoff valve inline.
The anti-backfire valve is not a "shutoff" valve as some people believe. It is only there to assist for quicker shutdown and prevent fuel from being sucked into the engine after the ignition is turned off.
From the sound of your situation, starting it on a regular basis while stored may not be a good option, due to having to tote a battery for some distance and then fumbling with connections in the cold.
If you have electrical power where you are storing it, a battery maintainer might be a good option.