Very cheap and durable would be ABS plastic of the appropriate diameter and length. But that's not very UL.
I snagged some plotter-paper rolls (like the cardboard tube inside a paper-towel roll, except it's plastic, stiffer, waterproof, longer and wider). 2" I.D. 36" long. 180 grams. So 27/36*180 grams = 135 grams / 4.5 oz in your length. I'd glue a test plug (translucent plastic disks with an indent sold in the ABS fitting section to be glued onto rough plumbing to accommodate a leak test and then be cut off) on one end. For the other, operable end; I'd use one of those flexible plastic caps found on a 6-inch-long tube marketed for storing screws/nails in.
PM me if that is of interest. If your garage doesn't have a zillion glues, epoxies, etc like mine, I could cut it to length and glue it up for you.