If you're just using it as shelter and not wearing it, why not just get a vinyl shower curtain? Completely water proof, cheap and you can get them in 6' by 7'. No hole in the middle and they're tough, hard to stretch let alone break. The only down side is they only have grommets on one side, but thats easy to fix.
_________________________
A gentleman should always be able to break his fast in the manner of a gentleman where so ever he may find himself.--Good Omens