66 Cab Upper Floor - Common rust area- Any mods or prepping to prevent?

[msg]

You see it all the time, the floors are rusted out where all that road crud spins off the front wheels and cakes on the cabs upper floor area. Im repairing mine now but in doing so I was wondering what flaw there is that might be corrected here. Was it just a not so great paint type they used? Bad seam sealer? Instead of having to be super diligent and wash off the muck often, is there a good approach to keep this from happening all over again?





Borrowing a pic from Racecougar on this one, hope he doesnt mind