Anybody use a Yakpak? I pulled mine out of the attic the other day...haven't used it since 1981. They were the precursor to Rivendell packs. No frame whatsoever. The load becomes the structure. I need to test this thing out again to see if that design works for backpacking. I believe they were more designed for climbers, but I could be wrong on that. Anybody have any experience with them?