* VirtualBox seems to allow mounting of USB devices (e.g. flash drives), but I haven't yet worked out how to get it to work... and I'm not sure if AROS would see it even if I did?
You are required to have installed the extension package in order to mount USB >1.x devices with VirtualBox.
In your AROS Virtual Machine you need to enable that USB support but, your mileage may vary wrt which USB-version works best for your setup. In my experience the smartest thing to do is to start with USB 1.x and work your way up and see what happens.
When a USB device is inserted at your machine the HOST os mounts it for you so that your host is able to access it.
Then, in VirtualBox, in one of the menu's there is a list of devices from the host that you can 'insert' into your (running) VM. You simply can select the device you wish to insert. Once the USB device is inserted into the AROS VM, then poseidon should be able to pick that up and automatically mount the device for AROS so that you can access it.
Having said that, do realize that AROS only (automatically) mounts devices that it is able to understand,e.g. FAT32 works but don't try a ext4 formatted USB device.
Does anyone have any other suggestions/ideas?
SMB is also an option. Icaros Desktop manual has a chapter about that, if not mistaken.
When i was using VB on windows I ran a second VM that ran a very tiny (non graphical) linux distro (around 80-100 MB) and installed the native VN extension package for that. That allows you to acces a host directory, which can then be mounted with using SMB, or you could run a FTP server on the Linux VM (but i guess the latter that will give you the same issues you have right now).
Instead of a second VM you can also use a small machine such as a raspberry Pi that runs in the local network as a server that can be accessed from the AROS VM using SMB. Having said that, i do not run AROS in a VM that often anymore as i prefer running AROS hosted.