Here in the North, the boating season is almost over and it's time to thiink about winterizing. I usually store the boat with the fuel tanks full to prevent condensation build up and add then stabilizer. Today's gasoline is so crappy, sours so quickly, and in our neck of the woods, has 10% ethanol added(attracts moisture) that I am thinking it would be better to leave them empty. Any thoughts?

If you have a metal tank I would store full but put stabalizer in before you put the boat away, if not then I would store with limited gas.

The last few winters have been crazy with huge temp fluctuations. If I fill the tank and a REAL warm day comes, the gas expands and spills out my vent. So, I'm just going to stabilize the gas that is left in there and fill up in the spring. I'm only winterized for about four months.

Always full and add stabilizer. Last year I also added a piece of pvc pipe to my vent and brought it out of the swrinkwrap , because every spring as the temps increased the gas would expand and run down the side of the boat leaving a mess. It worked out great.

Old school here, fill tank alittle over 3/4... to allow for expansion in the spring add stabilizer now and octane booster in the spring....

I have a built-in fiberglass tank. Prefer not to keep full over the winter as per manufacturer's recommendation.
I have an 12 VDC Weldon Fuel pump setup to pump the tank as dry as possible. I use to fill them up for winter storage.

Rlw the problem with that is you will get condensation ie water

Full, plus, its my 160 gallon backup in case of a shortage. Price will likely be higher in spring too.

I read a while back on another thread about the problem of gas coming out of the vent during storage. It is not the gasoline (liquid) that is expanding to any significant degree, but rather the vapor in the gas tank. Say you have a half tank of fuel and the trailer is cranked up with the boat is nose high. There is a lot of trapped vapor in the front of the tank that will expand on those warm days and literally pushes the gasoline out the vents. Putting the boat nose down so the vent taps into the vapor pocket allows it to "vent" (no pun intended) and you don't push liquid out. Makes sense to me... Just need to have the boat stored indoors so no other liquid (rain water) gets trapped into the nose down boat hull...

That's exactly how I feel! My tanks are aluminum...I have a problem putting "alcohol" in my aluminum tanks. Besides, your right about the stuff going bad so quickly! I have been stabilizing what is left at the end of the season (usually less than 1/2 tank)...fogging the motors...and hope for the best!