If you have the most recent version of the sonicTransporter it has a drive bay on the back. You can use that to add your own SSD for msuic storage. Start be making sure your sonicTransporter is off and unplugged. Then put it flat on its bottom on a table.
Slide the silver square to the right and the drivebay will open. Slide you SSD drive in and close the door. Then power on your sonicTransporter.
Using a web browser on your computer or tablet go to sonicorbiter.com -> manage (next to your sonicTransporter) -> Settings -> Drive Mounter -> Internal and select Format Drive Bay. This will format your drive for use.
If you don't see the Drive Mounter you can install it using the Software Manager in Apps.
Note: Files that that are already on your USB drive can not be used. The drive must be formated clean before you can transfer files to it.