For some reason, Storage Containers will not snap against the side of another, only on top/below. Quite annoying and with free placement making it hard to place it close without snapping.
Building a (temporary) 4 junction tunnel to access the storage vaults will line them up lovely.
If only I could … I do not yet have all the desired parts for that to work. Although, I guess a single straight hallway might work. Will have to try that, thanks for the workaround suggested.