Skirting a mobile home or an RV would be pretty much the same thing. One thing which is very necessary is venting to keep an air flow under the home.
My brother was in the mobile home business for several years and I worked part time for him when he needed extra help. I have seen some real damage done to a mobile home because it was sealed up to tightly underneath. I have seen the bottom side of the factory building board entirely white with fuzzy mold. If you pulled down a sheet of board it was soaked with moisture.
While bales of hay or straw look like a cheap alternative it really isn't. You have created a nesting ground for rodents of every shape, size and description. This also provides an excellent home for skunks. They thrive on the rodents. Pull a bale away from a mobile home and the backside of the bale will be white with mold and smell like S***. Try to discard 60 or more rotted bales in the spring when you don't want them anymore. Unless there is a mushroom farm nearby getting rid of the bales is nearly impossible.
2002 Fleetwood Storm 30H on Workhorse P32 chassis 8.1 gas.