My experience was with a 200 gallon bladder tank with diesel. I had it semi permently mounted in the bilge. This required filling the bladded thru the direct fitting on the tank inside of the boat. Slow filling was not a problem. I fitted a transfer pump to move fuel from the bladder tank to the fixed iron tanks. No vents are necessary. The tank was a heavy fabric with what seemed to be black Hypalon. It was purchased by the wholesaler who supplied Avon inflatables and I believe it came from the UK. I lined the bilge with ozite carpet both on the bottom and on the top where any floor frames might have rubbed on the tank (The boat had a perfectly smooth fiberglass bilge in this area). I had epoxied pad eyes to the hull to secure the four corners. I used the tank slightly over 3 years. Shortly before we were ready to leave the Canary Islands for Barbados, at 11 PM I noted a strong smell of diesel. A small pin hole had developed. Using the transfer pump and some 5 gallon jerry cans I had a "Midnight fuel sale"--and we got all of the diesel out of the tank--the bilge was a bit more difficult, but there was only a couple of gallons. I put the tank in the trash at about 2PM and by 8 AM some one had picked it up. I have seen a number of sport fishers who use the bladder tanks to run down to Mexico across the Gulf,mostly from the Houston area. This is certainly better than 50 gallon drums on the deck. They have been used in both the cockpit and on the foredeck. Bob Austin