Is the leak from the sewage drain or the belly pan? Use your olifactory detector to see if it stinks. To state what you probably already know if it shinks it's @#$%. If it doesn't it's probaably grey water or fresh water and there is a leak in the plumbing. Does it only leak when hooked up to city water? After using the sinks, or shower. This should help pin it down. Finally get hold of a service (not owners) manual with a diagram of the layout of the plumbing. It could also be a leaky low point drain valve.
Sail on silver girl. Sail on by. Your time has come to shine.