Not knowing "how" you deternined there's a leak makes it difficult to comment.
Is there constant fuel odor coming from the tank area?
Is there run off in the bilge area?
Does the gauge drop down after a period of time in the driveway?
Have you checked all rubber lines to ensure "they" are not leaking?
How about leakage around the fuel pump itself possibly?
Check all other possibilities and everything that deals with the fuel before you go tearing up your deck, because the hard part is getting it all back in properly without professional help. You wouldn't want a new tank banging around in the rough with the family onboard.
Good luck with your project and hopefully it's just a hose.....