you certainly didn't get very good adhesion Jim, I know you live on the water (salt water) but if your not having that problem with anything else...then it must be the application in this instance...probably the paint, I see Keith Appleton uses etching primer all the time, I personally don't have any experience with that. I guess i wasn't much help here, but I know we have many members whom can guide you .
BTW ,how many mounting holes are drilled into that base Jim ?