Boraxed skins will work but plan to spend about 1/2 hr washing it under running water or the glue won't stick it to the bow, same with a salted skin.
I would soak your frozen skins for an hour or so before tacking them flesh side up to dry. while wet, use a spoon to flesh, pull the meat from the center of the skin to the belly scale area. You will cut off the belly scale part of the skin after it is dry when you remove it from the board.
For your next skins, roll them up, put in a zip lock bag, fill the bag with water and squeeze out the air. Throw the bag in the freezer, the water protects the skin from freezer burn, it will last indefinitely stored this way.