Generator quiet box plan

So i buy all this stuff.

I put the generator and the extra fuel tank in the box. Attatch the muffel thing to the generator (which is made for this generator). I drill a hole into the plastik box so it can go through it. From the other side i make holes with ventilation going in trough smth labyrinth like. Then i put this rockwool around the box and done. good? How much quieter will it be?