I get my daily drivers sprayed every fall with a Krown equivilant just as explained in that article and it really does help to keep cars from rusting. What makes it less suitable for Amphicars is that oil on any exterior surfaces will eventually wash into the waterways. If your bildge pump never runs, you could spray it in the bildge, cabin floor and trunk to keep those areas protected. My bilge does run or I would do just that.