Galvalume on the Gulf... rust??

hi, I have a townhouse in a 4 unit structure in mexico beach.
we are putting a new roof on, possibly a metal roof.
hurricane Michael did a real number on us but we are rebuilding the townhouse, its a common roof, no firewall separation up top. one of the tenants got a bid for a mill finish galvalume system.
in the bid there's an exception in the warranty against rust, we are 400-500ft from the gulf so well within the 1500ft no rust/warranty.
he says aluminum doesn't rust which i said is true, a solid aluminum
panel won't rust. i believe galvalume comes in different grades for the alum-zinc coating- i read the AZ55 is the best, but will it pass the grade against rust on saltwater??

salt water on the cost is one tough nut, especially as close as we are. the lower grade of stainless rusts in no time.
can a pro tell me more about the rust issue and galvalume systems.

I was a roofer for 30_yrs but retired when the metal roofs became popular in te fl panhandle, but during the building bubble metal systems exploded in the area. I saw a fair amount of rust issues on some of these roofs, some with obvious rust within 3yrs and complete replacement in 5-7yrs. colors are also a bad choice.
the deep colors--> forest green-deep blue-fire engine red just do not last, and roofs are being painted in 3-5yrs. I always recommend mill finish or a white painted panel because you can't tell when they fade. anyways looking for advice