Re: C Clip
When I first saw your pic I thought maybe it was off of one of those EZ up tents.
Your best bet will be to call the manufacturer, chances are they are having those molded just for that application. If you do get in touch with someone, make sure to get plenty of spares. Using plastic like that in a cold environment can't be good.
Other than that, I'd try to make something out of metal that will do the trick?