Thanks guys, I've been leaning towards a 20L, just wanted to double check. Although, if i had a large female, a 30 is also a good option too.
I know that Ball Pythons aren't really "display animals." What I meant by display tank is that I just want a enclosure where I can check up on it whenever I felt like without having to open a lid or slide a tub. Peeking at it from the opening if its hides and catching it roam around a little bit at night is all I hope to see.
My principle is that I want to keep things as simple as a tub but with the viewing capability. I don't plan on having anything inside the tank except two identical hides, a water bowl, aspen bedding, and a thermometer/hydrometer. Maybe a few branches. Would that be okay?