Here is my walkthrough of the campaign, part 3, that shows exactly where to get this achievement naturally.
1. This is after the diving section, and after opening the underwater door.
2. You will run into an above water door, that you must climb, get across a windy bridge, and go inside the mechanism in the door.
3. Load the garbage in the water onto the hooks, and feed them into the gas tank.
4. Get the fire to max heat. This will start a blue bar that is charging a button.
5. Douse the engine before it gets too hot, and keep the fire hot.
6. When it gets hot enough, a button pops out to open the door.
7. Life the module, that is above the engine in a sealed box, our of the door mechanism.
8. Carry it across the bridge to your boat, and install.
Hard to explain - the video makes a lot more sense!