Yes they are running in a container and yes I am able to log in as the amp user create folders and files in the /mnt/backup/ampbackups/ I made a testpermissions folder, then under that created a test document file
ok I think I have it sorted out, took a lot of manual editing (personal learning) and followed this guide for EACH instance, plus setting the token in the interface for the storage, took a few times to make everything stick. Probably me doing something out of order, but I have the backup menu and testing backups created where I expected them.