You can make this a lot easier by playing the Gib Fest mutation. I managed to get this in 12 minutes on my second try, on Single Player, Easy difficulty. The finale only requires 6 gas cans.
Some tips:
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Just keep running, don't stop for too long and try not to get surrounded or get pinned down by Special Infected too often.
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In the first chapter, memorize the optimal route for starting the generators. If you have a bile jar and/or adrenaline, you can speed thru this section.
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In the finale, after you start the generator, go and camp near the farthest gas can near the stairs at the cliff. So that you can immediately start juggling from there when the generator break down.
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After you filled the last gas can into the generator, you can start running down to the docks and camp there. Throw a pipe bomb or use an adrenaline to make things a lot easier. The boat will come right after you kill the second tank.