I am currently using a 15g glass tank and I want to switch my BP over to a larger plastic tub along with using a UTH instead of an over head heating lamp. Will this be good or will the UTH melt the plastic? I also want to know how many watts is good when it comes to the UTH, I was thinking 4 or 8 but i dont know if 8 is too hot or if 4 is too cool, etc.