I'm afraid to drill holes in mine in fear I might lose too much heat. I think the crack in the top is fine for ventilation, as of right now. As far as extra heat.. maybe you could plug the holes between the tubs or something so it holds more heat back in the tubs with frogs who need more heat. I really don't know about what you could do to get extra heat in a rack.

Edit: Just to clarify, for example, you keep your caatingas on one level and to raise the heat, you put a sock of some kind of insulation between their two tubs so no air escapes through that middle area, you could plug the sides too. I don't know if this is a fire hazard or not though, I'm not too sure how safe this heat tape is. It looks very well put together though.