Personally speaking get yourself some flexwatt...you can get it at reptile basics. Then get yourself a herpstat thermostat. Dump the rheostat. Then get yourself new tubs. I would think there is some type of failure with something that is allowing the temps to spike hence the marks and holes on your tubs. This could prove to be lethal to your snakes if you don't do something fairly quickly. I know that the herpstat can come in literally 3 to 4 days. If you call rich at reptile basics and tell him the situation....I am sure he will send you the flexwatt asap.