When I was in high school I read a book about PVC pipe being used to cache supplies as well.  The author stored everything from a break-open single shot .22 and several boxes of cartridges to camping supplies, etc., and had several buried all over.  There was a caveat, he said, with doing this - anyone with a metal detector and a little bit of curiosity could find your stash in the woods before you dug it up to use it, and he wrote this had happened to him several times.  I totally forgot who the author and what the title was though.  I was surprised enough that the book was in my high school library.  I should have swiped it when I had the chance...
Love the PVC chairs as well - looks like something my college buddies would do in their dorm.
THANKS very much for sharing Chisel!