Shims good idea
I would take Catalina’s advice and place some shims onto the bunk boards.The weight of the vessel should not rest on the swing keel. Such will place a very serious stress onto those four 5/16' bolts that support the keel and whose weldments are only encased in epoxy.The shims, which actually may be just some square pieces of possibly 2 X 4, should be placed between the trailer frame supports and the bunk board. In this fashion the bunk board and vessel can be raised while still maintaining the flexibility of the bunk boards.However, I personally do not see much wrong with the keel resting against the metal of the trailer. Perhaps a couple of layers of duck tape could be placed onto the trailer or even some thin indoor /outdoor carpet or even the materiel used to cover the bunk boards.