For the past few years I've been carrying my little 5-piece pack rod in a telescopic black plastic poster tube (branded MHWay) which I picked up in an art supply shop in central London.

It's 2.5" in diameter, very lightweight, complete with shoulder straps on each end... and now as far as I can tell out of production... which is a shame since I shortened it slightly to suit the 5-piece pack rod, and would love another one or two for other rods which are slightly longer. Fatter tubes around 3.25" are now available, but the slimline strikes me as better: you might want to keep an eye out for something similar?

Theo