I also had a surprise gas leak when I picked up my 2000 Monaco Diplomat last fall from TX. Every time I filled it up, it would leak fuel on the ground for a few minutes.
Turned out to be the vent line coming off the top of the fuel tank going to the filler neck. Replaced the line with a new one, and haven't had a leak since.
10/11 2000 Monaco Dip, 315 ISC, 2nd Class A, Me GL1800 & DW GL1800 Trike, 757 ret., 510 club