heating methods for 18x18x24 - 2 white's treefrogs

[Bolisnide]

You all have been very helpful a few weeks ago on advising a larger terrarium for my white's tree frogs and I have recently upgraded to an 18x18x24 exoterra terrarium.
I am really having an issue with keeping the enclosure at an appropriate temp. as my house is literally 60 degrees at night. I do have an 8x18 UTH mounted on the side of the tank, but need more heat! Currently the temps are about 72 during the day and 68 at night with the current set up. And they do not like the 50W red night bulb at all... in fact, it doesn't even give off enough heat anyway. I was advised at PetSmart to get a ceramic heat emitter of 150 watts. Which is what I came home with.... but, I came across a thread started several months (years?) ago about the same issue, but didn't find what had actually worked for this person and what she had finally decided to use. And also found that many here felt ceramic heat emitters were no good for frogs.
I was curious to know what recommendations you all would give after your own experiences. I don't want to cook my frogs!
Thank you for your time,
Lindsey