got it guys. thanks again.
i will side mount the heater and see how it goes temp wise. metree, you said exactly what i wanted to hear about the burrowing.

this is what i found at joshsfrogs
"Many people recommend keeping a water bowl in with the Pac-Man frog. I have kept Pac-Mans with and without water bowls. As long as you keep the substrate moist, a water bowl isn’t a necessity.It is widely circulated that Pac-Man frogs need temperatures in the 75 to 85 degree Fahrenheit range. While this is true of their natural environment, Pac-Man frogs spend the majority of their time buried in the cool ground. In captive environments the substrate doesn’t provide the same protection due to lack of depth and the ability for air to move under the tank. Therefore, normal room temperatures of 65 to 85 degrees are recommended."

reguardless i will get the temp to 80ish and i still believe in a water bowl.