The Progressive Dynamics has fuses onboard and I don't see any mention of adding additional inline fuses in their manual.
However, adding fuses between the batteries and the system is a good idea. I've seen these called 'catastrophic' fuses before, with the main goal to protect things if there is a dead short somewhere. With lithium batteries this is even more important in my book since they have a potential for very high current on a dead short.
My understanding is that the ideal fuse is a class T since it will blow quickly and cleanly. This fuse should be close to the battery bank. Sizing the fuse depends on how big your largest load on the batteries will be, not the size of your converter. In your case with one battery, you still might have a load larger than your converter if you use an inverter, so check to see what your largest combined load might be when sizing the fuse.
There are class T fuses made in sizes less than 300 amps. There are a few size categories, along with a few different physical sizes for the fuses. I've got a Blue Sea fuse holder in my trailer, and there holders are sized to hold either 110a-200a fuses or 225a-400a fuses. In your situation, you could likely be fine with the smaller Blue Sea fuse holder.
Using one of their smaller fuse holders would allow you to put a 110a fuse in to protect the system.
Another option is using ANL fuses, which are available in a wider variety of sizes.