I put all three U Bolts in.  I would hate to put a cleat on the breast hook.  I was thinking maybe modify the inwale a little bit and install two sets of small Pop up cleats fore and aft.  Like maybe fill in the spacers with the same wood material and maybe build it out a bit as well.   But, I think you are right and the U Bolts should suffice for tying up to the dock or anchoring.  Less hardware the better!

The included photo show the hardware installed on the breasthook of my Peeler (prior to adding a u-bolt to the stem for hauling onto the trailer).