What you're experiencing is normal; just don't fill your tank to capacity the way you would your car. Automobiles don't have the sloshing around of fuel that is experienced in a boat and they do have far more sophisticated venting and fuel recovery systems.
The vent caps are designed in such a way that they do effectively keep the water out while letting air in/out. Do not tighten them down while you are running the boat. They need to be unscrewed just a bit and the notches on the cap and vent aligned to do their job.
me!
