We used to use a curtain rod in doorway stage when my kids were young but they kept leaning on the rod and it would fall down.  I was thinking of putting a rod across my narrow front porch for Halloween but I bet it would keep falling down too.  I guess that will teach the puppeteers good technique to not lean on the stage.

You know there are cloths rod "holders" you can buy at the hardware store that could help this. They are normally plastic and you use a screw in the middle to attach them to the wood. Then the pole rest in them.  You are right though that it should be good training for a puppeteer... they really should not be leaning against the play board.

I have used the shower curtain rods that are extendable. They can be purchased at Bunnings or harware stores. They hold up to about 7kg and are telescopic. You pull out till both ends are snuggly in door frame and twist to lock in place. Super easy!

You can make a folding PVC stage. It stores flat with curtains attached.  Very simple and inexpensive.

A tension rod in a doorway works too.  If you twist the rod until its tight it should not come down (unless children try to do chin ups with it)!