I made myself some very safe cases. Want to share it with you. 
Very nice! I made a similar case for my longbow (just a little bigger).
Did you put foam in the short tube, or is it just open? I’m thinking that you could cut down the longer tube so that the total closed length is the length of the whistle plus end caps. Then when you place the whistle in the tube the mouthpiece would stick out when you open it (so you don’t have to dig in or shake the whistle out).
Mike
You’re absolutely right. I should shorten the tube.
You see it in the video. No foam in the short part.
Thank you.
It needs some ventilation or you will risk some mouldy whistles.
I want to use it only for carrying. Not as a permanent case. I think the one for my fiddle is okay because of the missing moisture. Or could there be a problem, too?