[hiredhand]

IF the contents of the tube are properly protected, PVC will "do the trick", but you are correct about the gas permeation from the plastic. Do you know of a good source for sonobouy tubes?

[300winmag]

Do you know of a good source for sonobouy tubes?

Unfortunately, I haven't found anything recently, even with the help of search engines. This is stuff you can pick up at gun shows, but there's always a couple of BATFE agents and their snitches there, even the small ones. You might look at "military surplus" stores, although our military produces very little "surplus" any more.

A good discussion (and some possible sources) is Survival Blog discussion on caching.