Hello, I noticed in your post you mentioned that you have them in a 10 gallon divided by screen. If they can see each other it may stress them out so you may want to use something that isn't see through. And you want the divider to be sturdy and be right down to the bottom of the substrate touching the glass. The guy here at our reptile store use to keep his like this with the divider and it wasn't far enough down one time and the smaller frog buried under the divider and ended up on the bigger pacmans side, well you can probably imagine what ended up happening. The one ate the other. And to be honest the size difference between the 2 wasn't a lot, and I know this happened because I was the one who asked to see the frog that got eaten that day and that's when we put 2 and 2 together. For the UTH's I would have to agree with Jason that unless your frog/reptile room is already at a temp of at least 75f a heat matt on the side isn't going to do much to your ambient air. I use this method and it took me awhile before even getting frogs to get the temps right. Its not worth the headaches, it can be done and there is others that use this method but IMO getting a light or CHE is the easiest and most headache free way. Yes you have to mist abit more often but all and all unless you get a fogger its something your going to have to do anyway.