coating it with anything helping stop, block, corrosion, will make the trailer last longer and easier to maintain later. Fluid film is thin and will require a yearly application, wool wax is the same product only thicker, still needs reapplication. the newest kid on the block is Surface shield from the people that brought us PB Blaster spray penetrating oil. they say it lasts 2 years between applications. it wont hurt, can only help.
you spent how much on a trailer, or vehicle? a few hundred up front, and 50 a year to protect it, is well worth the time, and effort. Ski