haha had the same idea if you look back in the 2011 tuna thread....my thought was to have a rope running from the stern cleat to a forward bow cleat. Every 10" or so I thought of rigging a large carrabeaner onto a short length (6" or less) of rope, which then is fixed to the stern to bow rope....catch a tooner, stab em good, and clip the carrabeaner at the base of the tail. The tail is strong enough to not slip out I'd reckon, and then you would just have a meat rack of 8 or so bleeding tuna hanging off the side of your rig. Once they have bled out unclip em and toss them in the ice chest.
I may have been roasted a little with the idea, but I still think it would make a good system. As well as the removable ice chests built to the same size and shape the deck....10" tall and strong enough to stand on. Basically building a second floor under which you can store a shat load of Toons and ice.
But all in all I think Tuna Don has the best method, using aerated bait tanks with constant pumping water until they bleed out.
BANG BANG