For what it is worth . . . . we had very slightly raised deck water
fills. I made a little filter that fit down inside the top of the fill, we would let a hard rain clean off the decks a bit and then I would put a wet towel behind (aft of) the fills to create a dam, and the water just poured into the tanks
on a hard rain. The heaviest/biggest particles would stop on the deck
around the slight raise part and the smaller particles would get caught in my deck filter (and we had a charcoal filter at the galley
sink tap for extra clear drinking/coffee water).
It was super simple, worked really well, could catch 100gals easy in a tropical rain.