I went round in little circles. Here's my solution. This applies for Linux Ubuntu variants including Mint as well as the Apple Ipad.
First turn the router off, then connect the storage device. I connected 2 x 1TB western digital drives via a USB 4 port splitter. Both are formatted NTFS. Neither have a boot sector or any OS directories (folders).
Then turn the router on. After about 2 minutes it sees the drives.
Then on your computer File Browser type in SMB://192.168.0.254/ or whatever your router's IP address is. Your netpath is then visible for browsing and mapping to a drive. In my case they were USB1 and USB2.
In order to access them from an IPad you need to download Remote file manager basic (free).
Windows 10 has an issue with SMB protocol and I have not yet found a way round it.