This is the most common version that I know of that seems to match up with what you are describing. I have used them with large sheets of plex to create a barrier (obviously not a climate control version like a real vitrine. They offer the advantage for small museums of being able to break down the sheets of plex and reuse them later. Another nice thing is that if one panel gets damaged you don't have to replace the whole enclosure. Also if you need to change dimensions it is easier to cut down a sheet than a box!
They are really store fixture items but they can do the trick for some things.

http://djestorefixtures.com/glass-cu...fmtqt9fdeu5c93

Good luck!

Ashley