Maybe check the rubber "O" ring on your deck fill cap once in awhile. A little silicone grease helps keep them supple to.These days all larger commercial vessels use centrifugal water separators for filtering their fuel and bilge water. They are readily available but aren't cheap.
I really don't understand why you feel the need for something like this, as most marinas in North America only disperse well filtered fuel and even down here in the West Indies it's a pretty rare thing to get contaminated fuel. If you are getting a lot of water in your fuel, perhaps you should be looking at your system and not where you are getting your fuel.
Once you gravity 'drop' the visible water, consider to occasionally use a 100% CELLULOSE filter 'loaded' with the 'starch' hydroxymethylcellulose (the stuff used as a 'dehydrant' in baby diapers) ... will remove the emulsified and molecular water that migrates into the tankage from the tank vent to VERY low levels - most ethical fuel filter manufacturers sell them. Best to use the water absorbing methods in the spring and before the boat's engine becomes 'active'.Being a full time liveaboard in the northeast- with the cold winters, I get a bit of water in my fuel tank. This past summer I built a fuel-polishing system - have to look for a photos. Use a Racor 500g, Walbro pump. the first thing the fuel goes through is a solids/water separator.
Use this one- Diesel Bio Diesel Pre Filter Water Particulate Trap Sedimenter with Drain | eBay
When I first used it- I filled the bowl with gummed up algae and water Twice- before it got to my Racor. Works great!
Once you gravity 'drop' the visible water, consider to occasionally use a 100% CELLULOSE filter 'loaded' with the 'starch' hydroxymethylcellulose (the stuff used as a 'dehydrant' in baby diapers) ... will remove the emulsified and molecular water that migrates into the tankage from the tank vent to VERY low levels - most ethical fuel filter manufacturers sell them. Best to use the water absorbing methods in the spring and before the boat's engine becomes 'active'.