Heat tape running wide open isnt a smart option to start with.
Remember your temperature on the tape is going to be a little lower than inside the tub so you will still need a non contact thermometer to check your tubs.
Not only are you placung a value on your reptiles but also your safety.
You are being given a lot of good advice here.
And no belly heat is not NEEDED but then again back heat isnt either if you heat your room.