Joe and Erik are correct. As full as possible with some fuel stabilizer mixed in, your gas will stay in good condition for at least a year and perhaps longer depending on a number of other factors.
If there’s headspace there’s air, and where there’s air there’s moisture. Upon weather changes that moisture will condense inside the tank then drip down into the fuel.
So if I store my boat indoors where weather is not an issue, then moisture can’t accumulate, correct?
Also, I don’t need to use stabilizer because I exclusively use ethanol-free premium gas.