Below is a pic of a Scotch mailing tube, which is the closest thing I've found that seems like it has "possibilities". I will probably try Moray's rolled paper idea 1st, then try to find this Scotch tube as a single at a reasonable price, which is easier said than done, most places want you to buy a case! (a mailing tube would hopefully be sturdy enough to hold up long term)
And, I didn't buy the whole 4" tube from parts express, only the flared end. (it was CLOSE, but slightly too big) I may try to put the flare on the inside end to cut down on turbulence, especially if it fits snug on whatever tube I end up using.