We took the model into bigger waves. These were at least 15 inches which is like 15 feet. For the Caribbean this is storm or hurricane waves. We forgot to put sand in so it is riding higher than optimal.
Next we tried a string between front floats and also between back floats and strings from float to the opposite bottom end of the box. This works rather well really.
Next we tried connecting the two front legs together and two back legs together and attaching them so they can rotate relative to the box. Also put the 4 side strings all to a central point under the center of the box. This did not work so well as the box swung side to side.