I also agree that it looks more to be burns than rot. My orange ghost had a few spots of rot on his belly when i got him and I kept everything dry and after the next shed it went back to normal.
But the belly pictures above definitely do not look like rot to me.
Are you running a thermostat/rheostat on your heating device soph?
What kind of heating device are you using? And what temps do you have it set to if you are using a thermostat?