Here's a million-dollar idea, free of charge: heat mats with built-in thermometers.

The primary reason I stay away from the heat mat/thermostat combo is that I need a thermostat for each one. In order to use the thermostat effectively, I need to find a way to run the temperature probe inside the tank without creating an escape route for the snakes. It's just too much effort.

If I could see the temperature of the heat mat (without having to place a probe underneath, which would put undue pressure on the glass), then I could draw a correlation between mat temperature and viv temperature and adjust accordingly.