You want to fuse anything that has power closest to the power source. If the wire shorts out along the way you will want it to pop the fuse instead of causing a potential fire. When I installed mine I didnt read the directions, the black wire is the power and white wire is ground. Hooked it up backwards and the fuse popped at the fuse panel I have.
Best to add a fuse panel that you can expand upon. I have both fans in mine hooked up to the fuse panel I installed with, from my memory, a 20amp fuse. If one of the lines shorts it should pop the fuse. The whole fuse panel is then hooked to my aux battery with a breaker fuse, so power can be killed instantly to the panel and if tripped it can be reset once the problem is found. I believe I bought a 100amp breaker fuse.
Hope that helps.