Hi Ray
In my youth I sailed dinghies and didn't mind the occasional dip and thinking about it I would much prefer getting damp than hitting the hard sand at 40mph.
These are the details for the rear axle supporting saddle bracket.

Its a simple saddle bracket and could be made from any mailable metal or even an adapted plastic plumbing bracket, I specified the overall length at 70mm to minimise twist but this could be reduced to suit any available material.
Paul