Twin Keel vs Bulb Keel
Well not worried about movement as I would be welding some cross members also into the cavity to eliminate the chance of that. Not sure what the solution would be to eliminate any shrinkage.
I did mention I would be using 1/8" steel for the keel. I should have mentioned that it will be "stainless" steel with stainless welds. This will cut down on the maintenance.