Re: using 3M marine premium filler
3M Premium is a vinylester based product and needs to be catalyzed accurately to get optimal results. In small quantities this is next to impossible. When the mix is wrong you can get incomplete cures and/or excessive shrinking over time. Why not go with an epoxy mix, like Stumble mentions? Cheaper, better bond, more accurate mix (with pumps) and very little shrinkage.