I took a RotoPax to Alaska this past summer on my motorcycle. I had it directly mounted to my rear rack, and then packed an extra bag, tent, etc on top of it. I had contacted RotoPax to see if I could pile stuff on top of it without it leaking, even with big temperature swings. They said that they test them in the parking lot and drive pickup trucks over them. Worked great for me and seemed to be a quality product.
Same as oclv, these things are great. We use them on our GS bikes for gas and water. You can whip on them and they do not leak. The fastening system is bomber.
I use a 2.5 gallon water jug and the 2.5 gallon tool box on the rear rack of a Rokon 2x2 trail bike. It's been on a couple of years and has with stood crashes, tumbles and passengers riding on it. The cans and mount are stronger than they look.