Tony I would jack up the van on each side with the tire jack and reach in and
feel on top of the gas tank.  You should feel where the lines go into the
tank (trace from the plastic expansion tanks down to the main tank).  My bet
is that one of the two "T"s that go into the top of the tank are broken (very
common).  You can get this part at the dealer for under $50 and install it
without dropping the tank.
If you can't find the leak this way, then the next time you fill her up feel
up under there until you find it.
Hope this helps you and glad to hear you have a new beast of burden!
Ken Wilford
Van-Again
John 3:16