Bob. In this case (and I forgot the hull was so thin)..how about trying out some temporary large bilge keels, use waterproof tape to fix them on. I know you know what a difference they make to the rolling of a vessel. of course you may still need more ballast but then it will not be so desperate to get it under the boat.
I have reluctantly … on several thin boats (TBD,T22 and sub, for instance) glued strip steel, about inch by 3/8 section underneath, to get some stability as I like to be able to play in the rougher blowy weather. My boats are all flat at the bottom and it does not show.. however this sort of thickness would not show much in any case and can be run full length..on a sideways look you would not notice it esp if the ends were tapered somewhat. Another advantage of this is the generous contact area, especially relevant to your thin hull,.
Ashley
Ashley