I've been selling on eBay for years and I use mailing tubes in 50% of my shipments and I process the payment for Canada Post through Paypal. Most of the times I use Small Packet Airmail and the minimum package width is 9cm, so I based the size of the mailing tube from this, that is any tubes with minimum diameter of 3 inches (and I put 9cm in the width field for Canada Post shipping on Paypal's site). I do on average 30 shipments per month and in the past 3 years only 2 shipments didn't arrive at the buyers.
There is a problem though: Small Packet Airmail = no tracking. A kind of tracking number (I call it Dummy Tracking) is provided by Canada Post but it's only to confirm when the postage is purchased online, not even to confirm if the item has been delivered to the post office (after you hand in the package to the postal staff, then it's all dark! -- crossing your finger wouldn't help at all). Services that provides tracking cost twice as much (if not more). If I use this kind of delivery service, I won't be selling anything at all because no buyers would be willing to pay for it. So I think I've been lucky (but for how long?).
