I was going to wait on this one but have time to go first;
On Long Island, I don't consider humidity a problem until the spring, especalliy since I'm not done until end of Oct using fuel. And back in the water by late May or so when humidity does pick up there on.
More humidity = more condensate can form day to night as air moves in and out of fuel tank naturally.
Presuming the gas O ring cap seal is renenewed periodically and no water coming in. Condensate forms on the inner walls of the metal gas tanks particularly and the fuel's temp itself effecting the tank temp.
So for me, it's treated fuel with Marine Stabil regular dose is good for 6 months I believe, up to a year with higher percentage. All fuel going into boat gets Stabil, I add Ring Free for another reason.
A full (not topped of) tank is safer to be around since less gaseous space inside tank (fumes or vapor ignites not liquid fuel, and gas flashes at room temp unlike diesel).
This last year was first time I didn't fuel up, had no issues.
Others fuel up to hedge a risk against rising fuel prices come spring, as I had lost out this year spring big time since much higher price than fuel in fall. How ironic since always fueled up in fall.
I buy fuel at local gas station via portable tanks. No extra runs just do it same time as car is fueled, usually don't do it until later Nov/Dec.
Marinas may call for fueling up due to safety concern of vapors in not full tank.
So for me, if I think gas will rocket up come spring may do it in fall.
Either way works for me.
As far as going empty, you have to suck out all the fuel via level sensor port as the fuel remaining will still be plenty via normal pickups. If you suck out this fuel, you will not see water but the phase separated mixture that in my experience is darker than new fuel which is a lighter golden color, not darker.
It's all I look for in clear separator bowl, abnormally looking fuel color of any color or clarity. Found no corrosion in HPDI VST tanks, so far.
