You can see the tool box across the gap when you first enter the lower decks. To get there isn't that bad once you understand how the place is setup. Bring oil and dynamite for the boss fight and remember to DO NO DAMAGE when they have the red shield up.
To get across the map, think about it as a letter U. You start in the upper left side, you have to get down to the bottom, cross the zone, and then make your way back up.