if its a plastic based fabric i would go with melting a hole in it. I dont mean just stick a lighter up there and let her rip, but find something metal that is reasonably the size you want, heating it on a stove and the letting it melt its way through. That way you wont have any unraveling of the material. Otherwise you may can find a large hole brass gromet kit that you use to repair tarps. That might run you 8 bucks or so, but it would be a professional looking hole.