hi James,
Not sure which wrecks or what charter,but smaller knife jigs around 150gm work pretty well on a variety of wreck dwellers like smaller trevally and amberjacks. Cobia are generally a bit random, we see them on the wrecks south of yeppoon mainly in oct nov but a chance anytime.
big blades/vibes are also a lot of fun.
We mainly catch cobia by pitching a big plastic or bait at them when they swim up to the back of the boat.