When you have a fuel tank leak, one of the biggest problems is to identify where the leak is located, because it could be located in the fuel pump, and not the tank.  Also, some fuel leaks occur between the gas cap and the area right beneath it.  There is a huge article on this link, about fuel tank leaks: http://www.aya.org/aya.aspx?pgID=1035.  This is a fairly serious problem and many of the auto web sites say that there is very little room to work around the fuel tank area.  You might want to think about having this kind of repair done by a professional.  If not, get all of the advice you can, from the service department of your dealership, first.