I always go super simple for the QT tank. I bought a cheap Rubbermaid container and punched holes in the lid. Put a couple paper towels (the kind with no prints on them) in the bottom and soaked them in treated tap water. A small 3" pot with some pothos clippings in them with a heat source. The great thing about going simple (paper towels substrate) is that you can easily tell if the frog is pooping regularly. You do need to change the paper towels daily to ensure the frog is in a clean environment, but totally worth it.
Here is what mine looked like front he outside and then a top down view of one of them. Super simple. Not pretty, but functional lol.
The Red eye tree frogs that were in this to QT tanks lived in there for nearly 3 months while we waited for them to get big enough to move in with the other Reds we own. Just as an example how long they can remain in a simple setup like that.