The last time I was backpacking in Yosemite I saw a guy with his BearVault strapped on the outside of his pack—and the BearVault was empty! Of course I asked him about it.
He explained that it didn’t really fit well inside his pack, so he just stuffed all his food into a plastic garbage bag in his pack (no problem fitting that!) and then carried the BV on the outside, as if it were a Zrest mattress or something. When he got to camp he put the food into the BearVault, and everybody was happy.
I’m not sure I’d want to travel that way, but I do give the guy credit for thinking outside the box…or the backpack!