Advice on substrate for RBI 2x3

Hello everyone! I am getting a 2x3 Reptile Basics display cage for Charlie. I have been trying to figure out what to use as a substrate. I have been using newspaper in the CB70 rack for years now with moderate success, no worries about ingesting anything. But when they do use the potty it nearly always ends up getting all over the floor of the cage as the newspaper is easily moved around.

So in the new cage I was thinking about not using any substrate at all. What do you guys think? For anyone who uses a Reptile Basics display cage or anything similar, what substrate do you use? Thanks for your input.