I have a tandem aluminum boat trailer with stainless steel fittings,
torsion bar suspension and stainless steel brakes, and a variation of
"bearing buddies."

I regularly dunk about 75% of the trailer in the drink when launching or
retrieving my trailer boat. I wash the boat after every use, and while
doing that, I rinse off the trailer, especially the wheels and brakes.

There is no visible rust anywhere on the trailer. ...

Good to hear that. Seem like the aluminum and stainless steel
materials really help, especially if we wash the trailer after use.

Unfortunately, the trailer comes with the second-hand boat, and I don't
really have a choice here; otherwise, I would have chosen an alumimum
trailer.

The frame in my trailer is made from galvonized steel, and the
fittings are regular steel. The galvonized frame is still holding up
well. But the steel fittings (such as U-bolts) are all covered with
rust. I am thinking of spraying them with some kind of
rust-removal/primer chemical (no sure what it is?) and hopefully get
the rust under control. If this doesn't work, I may need to replace
the rusted fittings with stainless steel fittings in a case-by-case
basis -- or replace the entire trailer (depending on the available
budget).

Galvanized boat trailers do fairly well with the same kind of care,
except...you cannot see inside the steel box tubes that make up the
frames, so you don't know what is happening in there. Also, steel leaf
springs typically rust up no matter what you do. That's why I went with
aluminum and with torsion axles.

My trailer also has an torsion axle. But it is covered with rust (just
like any other fittings in this trailer). Oh well...

Anyway, I will wash the trailer with freshwater whenever after it is
submerged in sal****er. Hopefully, this can extend the life of the
trailer.

Jay Chan