First, Water normally comes off the A/C. drips down on the roof (or optionally runs down a pipe) and hits the ground (Sewer).
Do you mean you have a lot of water coming INTO the motor home?
Two things I have found that cause this.. One BIG TIME, one not so much.
First: On one of my A/C's the "Drip Lip" as I call it is to the rear.. If I "level" about 1.5 degrees "nose down" the drip lip can be higher than the inside edge of the drip tray and guess where it drips.
But the big time cause was dirty intake filters.. Yup, the big blower generates a vacuum in the intake area and sucks the water out of the tray up to the area over the filters,, Then when the blower stopps NIAGRA FALLS..
Clean the filters and teh vacuum is broken, now the water goes where it is supposed to.