Do I need to fuse batteries in parallel?
Remember that in a DC power system like you have, fuses prevent electrical fires by protecting WIRES, not the devices connected by the wires. This is not to say that blowing a fuse never prevents damage to an attached device, but that the "correct" way to think about circuit protection is to examine the circuit topology and identify faults which could result in a "wire" being subjected to current (and hence temperature) sufficient to start a fire, either in the insulation or in a device connected to the wire in question. This includes all fault modes identifiable. In particular, this includes at least damage to insulation from abrasion, thermal stress, water absorption, and chemicals (oil, gasoline, solvents), also parts and tools being dropped into a panel or battery box.

One other case to consider is that a fuse performing its act of protection can lead directly to a fault as well. If you have never seen one of the big T-series 400amp fuses go bang! you have likely saved pair of underwear. Fuses blow by melting metal, producing liquid metal which can be ejected to land on some other connections causing another fuse to blow. This is why fuse enclosures are worth paying to get quality products.