gauvins, last summer when I rode from Montreal to Ottawa but via Mont Laurier, I put my tent on the top of the rear rack, using these thicker webbing straps that I have. I have always used bungees in the past, but wanted to try these. They held extremely well, and never loosened once, but I think it was because of the thickness of the straps, so that they were not prone to slipping (but harder to slide through the plastic thing , for tightening)
It made it a bit harder to tighten, but I was really impressed with how they stayed tight.
I'll try to find a photo of them.
Just keep this in mind if you strap the barrel to your bike, non slip type straps like these will be a help.
I have a bag of various straps, and these ones were always annoying for putting around campmats or whatever, because it was hard just to quickly cinch them tight, but for holding my tent down, it was an advantage because they didnt loosen with lots of vibrations and bumps.