Hi Crocodile,
Ours on the Challenge camper trailer is the width of the camper trailer and press studs on below the opening tail gate. Ours doesn't velcros to the tent part of the camper but is pegged at the bottom to hold it down tight. The other side has a 'return' on it again with peg gromet to enable it to be pegged down and held in place.
The press studs used are the marine ss variety so that one part is rivited to the camper and the other side is fitted to the material part of the cover skirt.
If you (or someone you know) is handy with a sewing machine you should be able to make one quite easily from some silver tarp material. Simply sew on some velcro, The press studs are easy to fit and gromet sets are available at hardware stores or get SS ones through a marine boat cover manufacturer, on line or somewhere like "Whitworths" which deals in all things marine.
If all else fails, Challenge camper trailers in Adelaide have taken over cavalier campers and have an extensive manufacturing plant for repairs etc....if they haven't got one in stock they may be able to assist in making one up for you.
Good luck....
Sue