I suspect it was not completely dry before storage, or drew moisture during storage.
When you wash your "skirt" the next time, add a few ounces of bleach to the soapy water. This kills all the mold/mildew. To prevent re-occurrence, try treating it with Concrobium mold control
after it is completely dry.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"