Just a note when you come back to make a permanent installation -- especially where you need a screws worth of bite on a very thin water facing (heck any facing) surface:
I like wood so I use hard maple -- but completely coated in penetrating epoxy and covered again with unthickened epoxy, then physically epoxy and bond the backing block to your surface.
Now you have something to drop screws into , mount to , abuse, etc.... no impact to the hull. Not a perfect example, but attached is my backing block for my lower gudgeon from inside the hull:
I like wood so I use hard maple -- but completely coated in penetrating epoxy and covered again with unthickened epoxy, then physically epoxy and bond the backing block to your surface.
Now you have something to drop screws into , mount to , abuse, etc.... no impact to the hull. Not a perfect example, but attached is my backing block for my lower gudgeon from inside the hull: