We do not have any mass storage specific examples. The EZ-811HS kit (SL811HS dev kit) comes with sample firmware that provides all of the fundamental low level routines to enumerate and communicate on a low level with most all USB devices. This includes the routines to do bulk transfers that are required by the mass storage device.
You can take these fundamental routines and build upon them to create a "mass storage device driver". The embedded host will need to be able to implement file management and drive management. If you will be communicating with an IDE type device, the embedded host will need to be able to generate Command Block Wrappers (CBW) and interpret Command Status Wrappers (CSW) that the USB Mass storage peripheral understands.