“
Will a Bearvault 500 fit inside this pack laterally (i.e., not upright, but with lid against side of pack)? I have the older NimbusTrace (60 L capacity) and I have to put the BearVault in upright and it takes up most of the pack.
”

According to Bear Vault the dimensions of the BearVault 500 are 8.7 x 12.7 in. This backpack is 25 x 10 x 7.5". It appears that it would be about 2.7" too long to be able to fit laterally.