I lived in a mobile a number of years ago so I feel that I can add my 2cents worth.
Our mobile had insulation and a mesh kind of barrier to stop the insulation from falling out, but also to allow it to breathe,(I think).The only open spots under the mobile were for the pipes to let fresh water into the house, and the sewer pipe to let the drainage waterpipes out to their connection to the sewer pipe.
When we first moved in we did the check everything and it was obvious there had been a water problem. Where the drainage pipes were,the insulation was sodden.
We believed the washer had leaked,or the toilet had overflowed more than once. They were back to back with a wall between them.(toilet/washer)
First thing we did was,cut slits in the barrier to release the water buildup underneath the mobile.
Then we fixed the plumbing problems and what could become a problem.We caulked all around the bathroom and the area around the washer/dryer. Any water leak now could be quickly wiped up and not seep down under.
We were on a graveled site and were skirted in with plywood so we didn't have any water build up.
By the end of the following summer the underside was completly dry and we duct tape to reseal the cuts we made. I hope this experience helps you fix yours.
Maybe someone else can suggest how you can get rid of the water. You never said how much water there was or how it was being contained underneath your mobile.