As I was browsing the belly pan threads I ran across your post and was surprised that there were no suggestions.
Having done lots of antique shows over the years, I always had things stuffed under the tables (mostly new found treasures..). So, I know what you are trying to accomplish.
You could try a mobile home supply or dealership as they should sell skirting for trailers, either plastic or metal. You would have to construct a wooden framework, but it would probably look very nice. Or, you could build a wood skirt from T111 siding, a textured plywood with grooves to simulate individual vertical boards.
As a final suggestion, get some of the velcro pads with adhesive backing and some table drapes. Velcro the drapes around the bottom of the trailer.
Good luck with your Airstream and your show. My oldest son is an avid cyclist and advocate in Ft. Collins. He often camps in the four corners area.
Lew TAC #WI-6
Nobody can help everybody, but everybody can help somebody.