gas powered liveaboards...
In the days before electronic sniffers became popular, the standard test on a gas powered boat (or a boat with a propane stove) before turning on any electrical equipment, staring the stove or the engine was to sniff the bilge for gas fumes. You should not smell gasoline fumes period. None of the gasoline powered boats that I owned smelled of gasoline once they were put into shape.
You need to check the outside of fuel lines and the tank for pinhole leaks, (Tank will have dark mildew looking splotches and either the hoses or the tank will feel a little sticky)
Frankly a faint smell of diesel fuel is far more common on diesel powered boats than the smell of gasoline on gasoline powered boats. You can live with a little diesel in the air but you can die from a little gasoline in the air.
Good luck finding your leaks.