Mobile Home Skirting: At a minimum, skirting must be vented in all four
corners. A good rule of thumb is at least one square foot of open vent
area per 150 square foot of floor area. Keep in mind that vents with
insect screens, louvers etc reduce the effective open area of the vent
by 30-50%. Since you'll want insect screens and louvers on your skirting
vents, be sure to calculate the added 30-50% when determining the
number of vents you will need to install in your skirting.