I use a very similar system, but dont actually attach it to my pack. I use a foam mat to sit on, but just keep it attached to the bottom of my pack during transport.
when I\'m sitting/watching a park, I usually remove my pack (cause I\'m fiddling with stuff in my pack while I sit there).
still, this is a cool modification. I like the use of grommets for solid attachment.
That foam is great stuff! I carry a small piece rolled up and attached to my pack for comfort when glassing, resting, etc. as well. So light you don\'t even know it\'s there, but it sure makes a nice seat. Also glued a chunk to the top of one of my coolers and it\'s the rowers seat in my raft.
i carry a rolled up section of thermorest pad just with the straps of my pack. the compression straps. i just yank it out and sit on it..and then have my pack next to me so i can pull out all the crap needed to find an invisible tiny deer.