Not a junction box, its DIN rail mounted terminal blocks. The covered areas (solid grey covers) are wiring trays. These just clip on/off. The wires connecting to the terminal blocks have numeric labels on them. These correspond to the circuit numbers on a wiring diagram. Maybe someone here can provide you with a circuit diagram for a Maxim 38?
You are unlikely to find a "fuse box" on a boat. The "fuse" function is normally provided by the breakers in the breaker panel. There are also a few DIN rail mounted breakers in your picture.
The site I posted, just as an example, stocks many DIN components. You will have to search for your specific components. Google
"DIN rail terminal block" should get you started.
Do you have a picture of the fuel filter