Something else you may consider and probably much cheaper is a used billboard vinyl tarp. I just bought 14x24 for a flats boat I have for about $50 delivered and made my own. I invested in a $6 brass grommet tool and grommet package for tie downs. Pretty thick and can be patched easily with vinyl glue and left over scraps plus you can reinforce pressure points as well with the scraps. I live in the south and don't know how these would hold up for you northern guys with snow.
I got mine from this site:
http://billboardtarps.com/product-ca...llboard-vinyl/