I think that the NVG's are a great tool, but for night overwater operations, they are not capable of at producing a horizon 100% of the time.
Nothing will give you that horizon 100% of the time if the weather is bad - just like during the day.
You say you don't have an IFR option, does that mean you are not instrument trained or don't have an IFR equipped/capable aircraft or have other constraints that prevent you flying on instruments?
We operate low level over the sea day and night in all weathers but we have the advantage of a very good radar and radar operator which will allow us to keep clear of vessels/windfarms/land. We also have a very good AP and fly 2 pilot.
If you are flying overwater at night on goggles without a horizon because the weather is so bad then you are effectively in actual conditions. I trust you have a 4 axis autopilot with a rad alt hold and audio warner - plus a second pilot.