so it worked and failed.
i never really siliconed properly and in the center inside of box the cardboard has open edges. so had a little leak there.
tank was filled, and sealed everywhere else.
the plastidip did work. water never penetrated through, and even where the leak was, the cardboard still held even though half of it soaked up the water. the plastidip held the entire box together.
and no fish were harmed in the testing of this. all survived and were still very active in the the temporary new home.
i do kinda like how it looked and may try it again as i wouldn't mind having a extra lil tank for medicating fish.
So with my test Plastidip worked and was safe for the fish and fry.
i still don't recommend buying the cans, the one can i had took hours to dry, while the other within minutes it dried.
i always find inconsistency with using spray cans.