I know we often do things we shouldn't (me included) but Aluminium canisters would be worse to be carrying on your body, it would be a solid item to fall on.
Strapped to your bike would be okay
On longer trips (4-5 days) into the high country they are carried in the side pockets of my large camel back pack you don't even feel them and they are usually emptied asap , the spare tubes , tools , pump , clothes , food and rocks that you would land on would be just as painful if not more so , tried the bum tank on the rear guard works okish but restricts movement on the bike to much , bigger tank still doesn't cope with the longer distances on some trips so it is a necessary evil and there arent to many approved containers that will do the job.
