"What the best paint to prevent rust on top of the Matson box? "
Quickest way to rust one of those out is to paint it. Every one I've seen that failed was because somebody tried to paint it. The rust (maybe "patina" is more accurate) is a feature, not a problem. The more it rusts, the more rust resistant it becomes. Weathering steel was invented to be splashed with salt water it's entire life without rusting out. Once you take it out of that environment it should last decades past its "expiration date".
https://en.wikipedia.org/wiki/Weathering_steel
I knew somebody who bought one from the "experts" on Oahu that sandblasted them down to bare metal and then used their special "lifetime paint". The paint develops blisters (for lack of a better word) that traps water but also prevents the weathering steel from doing its job so it rusts "naturally". It started leaking in just a couple of years and they had to build a roof over it. They look all nice and pretty and white when they are repainted but its a sure way it will be full of water soon.
from the above article:
"a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance after several years' exposure to weather...painted weathering steel is no more corrosion-resistant than conventional steel, because the protective patina will not form in time to prevent corrosion over a localized area of attack such as a small paint failure..."
Quickest way to rust one of those out is to paint it. Every one I've seen that failed was because somebody tried to paint it. The rust (maybe "patina" is more accurate) is a feature, not a problem. The more it rusts, the more rust resistant it becomes. Weathering steel was invented to be splashed with salt water it's entire life without rusting out. Once you take it out of that environment it should last decades past its "expiration date".
https://en.wikipedia.org/wiki/Weathering_steel
I knew somebody who bought one from the "experts" on Oahu that sandblasted them down to bare metal and then used their special "lifetime paint". The paint develops blisters (for lack of a better word) that traps water but also prevents the weathering steel from doing its job so it rusts "naturally". It started leaking in just a couple of years and they had to build a roof over it. They look all nice and pretty and white when they are repainted but its a sure way it will be full of water soon.
from the above article:
"a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance after several years' exposure to weather...painted weathering steel is no more corrosion-resistant than conventional steel, because the protective patina will not form in time to prevent corrosion over a localized area of attack such as a small paint failure..."