Make some holes in the tubs. I like to use a soldering iron. Make sure you do it in a well ventilated space. You should be around 60% at times outside of shed.
More holes like Jamie said. Melt or drill a few...let the tub settle for a few hours...see if you need to do more. Also if your water dish is on the warm side move it to the cool side. If it's huge, make it a bit smaller (BP's don't soak so no need for a huge dish anyways). Also depending on where you live, find out the ambient humidity in the room the tub is in.