Your mate might have read a product review that I wrote for Gun Mart magazine last year. It's called a Pack Lounger, and it is worn like a conventional rucksack. There's a drop down seat pad that is normally held underneath by a couple of quick-release clips; when you want to sit down, release the clips and grasp the strap that falls down between your legs. As you sit down, you sit on the pad, with your back against the rucksack. It's really comfortable, and you could sit on it for hours if needed, and it is big enough for tons of gear and bunnies. It's great if you've got a dodgy back like me. Norman Clark the gunsmith in Rugby sells them for £48, and his number is 01788 579 651. There might even be a photo of one on his website, not sure of the address, but Google him and it'll come up.