I haven't packed meat out with mine, but I did pack my pop-up blind which is probably 15-20lbs and big and bulky. The Pac Seat has a strap that you can cinch down. You would drape your shoulder straps of your pack or in my case, my pop-up blind bag over the top cross piece and then cinch this down with the top strap. Fill your pack with the meet and then I would bring a couple of buckle straps or bungee's to secure the load on the bottom part that way. I wouldn't use ratchet strap as I wouldn't want to collapse the framing, just something that would secure the load that you can pull tight by hand would work.
Alternatively, this seat is super light so you could conceivably pack it on your frame pack and not feel it at all and just use it for its purpose as a seat and use your frame pack to haul the meat.