[cp4000]

I had a strong fuel smell in the cabin last year. Had a leaky STBD fuel filter cannister that allowed gas to seep into the bilge area which usually accumulates forward of the mid bilge pump inside the cabin. (Visibly, couldn't see any in the engine compartment.) Also had a leak on the PORT fuel filter at one point. My recommendation is to start at the tank and run your hand along the fuel lines / components until they get wet. Not as difficult as you might think. If I remember right, goes from the tank to the fuel water separator, to the fuel filter, to the fuel pump and then to the carb.
I suppose the fuel vent could be broken or plugged and fumes seeping out. (Spiders like the vents.)
At least a few ideas, good luck!