Typically, every manufactured home company requires one sq. Foot of free air to ventilate the crawl space for every 150 sq foot of floor area.
You need to be careful when you close off all the ventilation winter or summer, you will still get moisture in the crawl space in the winter, and if it can't escape to the outside, it will escape into the floor.
Please know the home is designed to perform without insulated skirting. Maybe your foundation it utilizing the insulation to prevent frost heave.
I would not put fiberglass in the crawl space, it can collect moisture and can cause problems with rodents,