Frame
The frame is the foundation for our house. If we want it to last another 40 years, the frame needs to be solid and protected.
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Outriggers
The outriggers are the steel supports that attach to the side of the main frame rail. They hold up the edge of the trailer floor, and support the distinct curved shape of the lower corner of the Airstream below the belt line. They also have a tendency to break, corrode, and generally need replacement after 40 years.
There are a few different kinds of outriggers depending on what side and position you need. Having these parts pre-fabricated would have been much handier if I was doing my own welding. Since I took my frame to a metal shop, it probably would have been cheaper for them to fabricate these in-house. If you don't need pierced outriggers, then an outrigger is just a piece of steel channel with the correct curve cut into one side.
POR-15
"Paint Over Rust" is a three-stage coating system designed to bond to rust, strengthen it, and prevent further corrosion. It's perfect for protecting the Airstream's frame. There is also an optional topcoat for exposed areas.
If I had to do it again, I'd use the black coating instead of the silver one. Apparently the black one has a thinner consistency which would probably have been easier to work with, and it's the one people use most often for this application. The color doesn't really matter because you have to paint over anywhere that sees daylight anyway. The unpainted parts that sat in the daylight turned an odd sort of green. Apparently the effects of UV don't compromise the performance, but it's not particularly pretty.
I used a quart of the degreaser (plenty), a quart of the metal prep (barely enough), three quarts of the coating (also barely enough), and one quart of the topcoat (plenty) to do two coats on the frame of our 27' Overlander. If I were doing it over again, I would have bought 2 quarts of the metal prep and 4 quarts of the coating and so that I could be a little more liberal with the second coat.