Yep, an all screen top won't help retain humidity so covering 2/3 of the top will help keep the humidity up on a tree frog tank. Darts on the other hand usually have almost all the top covered and humidity above 90 percent all the time.
The Glad Press & Seal will create the same results. Just what I will be doing on my Crested Gecko's Screen fronts (which will be poor for the view).