I used stainless steel bolts, with castle nuts and stainless steel hair pin clips for fasteners for the base plates on the toad.
Also used stainless pins with drilled holes for a lock on each pin.
The carbon steel base plate is the weakest link in the chain. The land between the holes, space, makes me nervous.
IF the toad is of an age that justifies the investment I would replicate the toad base plate brackets in stainless and be done . Pretty simple part to do. A reputable quality fab shop could do that easily.