Is there a way to contain fluorine gas for long term so that it can be visually observed?
As @JonCuster mentions, some materials are pretty resistant to fluorine gas at room temperature.

But out of curiosity, I checked Theodore Gray's website. He's made an effort to have a "periodic table" table with actual elements. He also has a beautiful book, called (naturally) The Elements.


  Almost anything placed in the path of a stream of fluorine gas will spontaneously burst into flame. This includes things like, oh, say glass, steel, and other things not normally thought of as flammable. It is, therefore, fairly difficult to have a sample of it in an element collection. I used to have a statement here that there was no transparent container that could hold fluorine for any length of time, but I was corrected by a man who has figured out how to do it.


There's more here but I'll summarize. Basically, the problem with glass is the $\ce{Si-O-H}$ bonds, which will auto-catalytically react with $\ce{F2}$ to give $\ce{HF}$, and that etches the glass. So with a high quality quartz tube, a lot of annealing, and a fluorocarbon grease to coat the glass and minimize reactivity, it works.

Interestingly, I always had the idea that fluorine gas was a light blue-green. Instead, it's brownish.