Before you can consider remedies you need to determine where the problem water is coming from and why it is standing under the home. Some possible sources could be: A plumbing leak or rain water run off from outside the perimeter of the home. Someone needs to go under the home and inspect the underside for dampness, dripping or water stains. While under there look to see if there are any tracks indicating that the water is running under the home from outside.
Even if you dont see any obvious leaks you could still have a plumbing problem. You should check to see if your water source is running when all water is shut off in the home. If you are on a public drinking system you can close every faucet in the home and all the hose connections and watch the water meter for a while to see if it is registering movement though the meter. If your on a private system again close all water outlets and listen to the your water system for the sound of water running through the pipes near the well source. If the leak is in the plumbing your pump will come on sooner or later to fill the holding tank. If you see the meter moving hear water movement in the pipes or hear your pump come on you know you have a plumbing leak.
To get a better idea of how to fix a plumbing leak when you find it read the free article Understanding and Installing Manufactured Housing Waterlines
If you see stream like tracks under the home coming from outside the home area you probably have a rain drainage problem. In that case you need to divert the water from running under the home. See the item about building a French drain
from a prior discussion thread
You didn't say where you are located. In all parts of the country there should be vents installed in whatever is skirting (enclosing the bottom of) your home. You local county or town building department can tell you how much ventilation you should require per foot of skirting. If you dont have at least the minimum you need to increase the number of vents, regardless of where your current problem water is coming from
Unless you are in a very wet, humid or extremely cold climate automated vents are not generally a necessity. My manufactured home is married to a block home on a hill side. The way it was set up it was only possible to vent 2 sides. One side is against the block building. The low side is five feet off the ground and the end that is uphill is only a few inches off the ground.
After several hot humid Florida summers we started to see tiny amounts of mold under the home. We installed an attic type fan-vent on the low hill side where the skirting is tall. It is attached to a thermostat / humidistat that turns the vent fan on when the temperature and humidity are within the range where moisture would get trapped under the home. In the summer it runs at least a few hours every day. In the winter we hardily ever notice it running.
To learn more about the site work that should go into any manufactured home installation you can DOWNLOAD Manufactured Housing Installation and Repair - E-Edition by George Porter
If your looking for an instant download that covers all facets of manufactured home repair see The Manual for Manufactured Home Repair & Upgrade
Let us know what you find out where the probelm is starting from ....