Hi sammyg,
Congrats on the new ElkRidge.
Custom skirts can be pretty expensive. A Google search on 'rv skirts' will turn up some vendors.
Some other owners have come up with homemade options. Hopefully they'll see this thread and comment.
If you're not moving around, it's pretty easy to make a partial skirt with 3/4" foam board and duct tape from Lowes or Home Depot. Putting it a foot or so inboard on the door side, and along the frame on the off-door-side will protect most of the plumbing. Cut it to size and shape with a razor knife. Put a ceramic disc heater inside the skirt and the underbelly will be kept quite warm.