Not unique to Rotopax. I also had trouble getting a Scepter can out of the holder this summer in the heat. They were jammed in there pretty tight. I will leave more air space next time I'm going to be traveling in high temps. Not sure if that will help any.
Agreed. The effect may be a bit amplified in the rotopax due to their thin profile (there is really only one dimension for them to bulge in) and the way their mount works. If the rotorpax mount is snug when you install them, by the time they have swelled it can be impossible to remove.
When they do bulge, I have had to vent them by opening the lid to be able to remove them from the mount. However, with buckland's mount, you wouldn't be able to vent them without getting covered in gas. On the plus side, they shouldn't get nearly as much sun, so they may not swell as much. Maybe lining the "shelf" with a 1/4 - 1/2 inch of foam to provide some room to swell but not to rattle when empty?
Not really relevant to the OP, but the other issue I have had with rotopax is their $#%^@# lock - it has rusted and seized on me (twice) and I live in a dry climate. Who uses ferrous metal on a lock specifically designed to be outdoors?