Becuase the holes are a bit low, it might hold humidity more than you'd like, I put all of my holes towards the top, and about 30 holes per tub, and still have really high humidity.
If you add more holes, try adding them at the top.

If you tape the heat tape to the tub, you will not enjoy cleaning them over and over.

You may want to put a board down between tubs and under the bottom tub, and lay the heat tape on that, so you don't need to tape it on the tub at all.

I do this same thing, but I use locking tubs that cost a bit more, but then you don't need to worry about clips holding the lid on either