Trap bungee - it sounds like a "return system" boat mod like this
https://www.hobie.com/forums/viewtopic.php?f=14&t=8001 and maybe here
https://www.hobie.com/forums/viewtopic.php?f=14&t=37051If you google it and search images you'll see some with those blocks under the side rails.
My boat, and most that I've seen, just use a simple straight line of about 8' of shock cord with snap hooks on each end. The snap hooks into a loop (bowline knot) in a small length of line that connects the harness handle to the wire like this
There are variations on this setup. The shock cord on my boat just runs straight under the tramp and around the side rails straight up to the handle. Some put them through holes in the tramp.
You are correct that the jib traveler cars on the front cross bar are connected by a bungee designed to snap them back to center after you release the traveler line.
https://www.hobie.com/forums/viewtopic.php?f=14&t=27447. I run mine around the dolphin striker one time just to keep it low and out of the way.