Where are you buying your gas? The only times I've had troubles with water in fuel is when I got crummy gas at the station. If you are getting amounts of water that are more than your water separator can handle, this suggests a pretty high volume source, which implies that the fuel being pumped in has the water in it. I try to make sure that I'm buying gas from a high volume outlet.

Are you getting any gas in the bilge at the same time? That would imply a tank leak, that could be a 2 way (water in, gas out). Sending unit gasket might be a place to look for that.

Had the tank pressure tested? Maybe it got installed with a metal scrap between it and the hull, which has pinholed the tank over time.

That's all I can think of. Good luck.