So, I just saw this on Deadspin.

It seems to me, this can be done cheaper by about $40.

Ikea has this backpack for about $11 or less (check sales). I have about 3 of these ugly things. But, these kind fold into little tiny sacks, as well.

To waterproof it, get some Scotchgard spray, less than $10, that can waterproof it. Done. Saved money over the good looking option that probably has better straps, too, as the straps aren’t nearly that nice, either.