"Any advice from the big Seacraft brain?"......you sure?
My brother's Hitchhicker trailer does the same thing. Between the tires and the new wood bunks we put on it floated. We completely re-did the whole trailer; sand blasted the paint off, new bunks, lights, guide post, tires/rims springs and axles. It does not seem to float as bad now. We are going to go with the 4" concrete filled pvc conduit wrapped to the frame channel until we get the weight right then replacing that with lead. If we ever get around to do it I'll let you know how much weight it took to keep it from floating. However they sure do tow nice!!!