I make Lexan (polycarbonate) "sleeves" for all my levels.
Polycarbonate Tubing, 5/8" ID, 3/4" OD for the 8" levels
Polycarbonate Tubing, 3/4" ID x 1" OD - for the 12" levels
Cut a strip out of the tube until it almost snaps over the vial. Heat it up slowly until its pliable. Snap it over...