Just to add to the pool of approval... I have been using tubs since shortly after I got my first snake. I only use flexwatt belly heat on a thermostat. I have never had any issues.

Is your husband concerned about a potential fire hazard? If the thermostat is controlling the UTH and keeping it in the low 90's there is no risk of it bursting into flames or anything like that. Especially if you are using a UTH and not flexwatt. Flexwatt gets much hotter unregulated than a regular UTH from the pet store does. That being said, a UTH will still get hot enough (unregulated) to burn or cook your snake, but not melt anything or set the plastic on fire.