Some good points that have been made.
US fuel tends to suffer slightly worse than UK due to storage techniques and climate.
Petrol suffers less than diesel from degradation through storage, however due to new legislation being brought in which will increase the ethanol levels within fuel, this will increase the fuels hygroscopic properties causing an increase of water and microbial growth. This legislation will come in power 2015.
Condensation as mentioned previously in fuel is an issue when storing, however I'll be surprised if it is significant enough to affect performance Just over the winter months. The biggest problem with condensation and water will be corrosion within the fuel system however this should be fairly minor if at all.
Finally as for products, the only one I would recommend would be 'aquasolve' it's a very very new product. It's perfectly designed for what you require.
I suggest you look at the website and information that is on there.
However as suggested, fill it up to the top until spring.