i've tried them all. with a gus too. i have friends who seem to like their "craw packs". you can run a search on that subject & find the info you need on that.
personally, i'm backing using a "fun noodle" (cylinder-shaped foam-tube pool toy; $2 at Kmart.) along with a 9' cam strap. that's it. on a brutal 10-mile hike last week, i was wishing i had my noodles instead of another system. i'd suggest at least trying this before spending loot on something else.
here's how it works:
1. lay the gus on its hull & stand at the stern.
2. cut the noodle in half lengthwise so you have two 3' mini-noodles.
3. run the tail end of your webbing through one of the noodles. pull webbing through til you get within a foot or so of the cam.
4. run the tail end of webbing through both cut-outs / holes in the back of your seat & out of the cockpit on the "other" side of the seat.
5. run the tail end of webbing through the second noodle.
6. run the tail end of webbing down through the stern grabloop & then into the cam.
7. adjust the system so that both noodles are against your seat, protruding out of your cockpit & down the stern deck of your boat. you'll need to play with the slack in the webbing to get a good fit.
8. to get into the "pack", stand the boat up against a tree/car/whatever & squat down. put one shoulder into the device & use that hand hand to push up against the front of your cockpit rim. then just throw your other shoulder/arm through.
to make it deluxe, wear your rescue vest while carrying to pad your back, but remove the rescue belt from your vest. you can run this through the safety grabloops just aft of the cockpit. this will serve as a waistbelt for your system.
til something else works better, this is what i'll use.