If yours is like mine, one of the weak points in the 34 design is that the shaft logs are immediately underneath the fuel tanks. I have PSS seals and while they are dry for the most part, they do put out a small spray of salt water which then contacts the bottom of the tank. I had surface rust as well on my starboard tank and used the POR-15 system to paint and treat that area. So far, it has worked very well.
Luckily, I can see all of the sides of the tank and the tops and sides of my tank do not have any rust issues.
I say “tank” because a previous owner replaced the port side tank with aluminum but the starboard side is still original steel.
I ordered the three parts (cleaner, metal prep, and POR-15) from Amazon. As has been stated, the paint does not last long after you open a can so I ordered the six pack of the small cans so I can use one at a time. The unused ones, I store in the refrigerator which is supposed to help with shelf life.