I have a 200 gal diesel tank on my boat. I will be welding from the inside. This is the only way. Tank is dry and wiped clean at this point. Next I am thinking about a water based cleaner with a mop and sponges on all sides. A soft wire brush would be next. I will need to remove a baffle with a jig saw before welding. I will be ventilating at 1500cfpm and I will be using a hookah for breathing. Does this sound good so far. Come welding time I plan on using the hookah for air. Do you see a problem with using co2 to purge the tank before and during welding. Boat is in the water and the tanks are built in and are part of the hull and bulk head. Everything is .250 aluminum.