Preventing Condensation Under My Mobile Home?

Today's Homeowner has a wonderful article about this:

Not Enough Vent Space: You may need more ventilation in the crawl space. The rule of thumb is to have at least one square foot of vent area for every 150 square feet of crawl space.
Inadequate Cross Ventilation: You also need to have adequate cross ventilation with vents on all sides of your house, not just two.
No Plastic Ground Cover: The plastic sheeting should be covering the ground of the crawl space, to keep moisture from coming up through the soil, not stapled beneath the insulation.

Leaky or Uninsulated Ductwork: If you have ductwork for your HVAC system under your house, have it inspected for any air leaks, and to make sure it has enough insulation to prevent condensation on the outside of the ducts when the air conditioner is running during the summer.
Add Fan Venting: If youre still having problems, have a small fan installed on one of the vents with a humidistat set to turn the fan on at 70% relative humidity to remove excess moisture from your crawl space.