I thought I would share what I have used to give black walnuts a kick start in our area. Not exactly tubes, but I use anything I can to shade the seedlings on the south side and they take off fast. Emerging seedlings that aren’t shaded can stay runty for a very long time.
Old junk vehicles work great for shade. They anchor nicely too 
I use pallets too. The seedlings in the foreground grew up enough that I removed the pallet.
