I know that aluminum will corrode (which is the same oxidation process as steel rusting). Aluminum is actually more reactive than Iron. The difference is that iron oxide is very brittle and doesn't adhere well to the parent iron. Aluminum oxide is extremely hard (it's often used as an abrasive) and adheres very strongly to aluminum. So steel oxidizes, but that oxide is porous and the steel underneath continues to oxidize. Pretty quickly you'll have serious pitting or perforation. Aluminum, on the other hand, oxidizes much faster than the steel but a microscopic layer of aluminum oxide quickly forms and protects the aluminum underneath from the atmosphere and the corrosion stops. You can take two identical placards of 1/4" steel and aluminum, drill a hole in each one and hang them from a dock on the seaside. In a few years, the steel sheet will probably be gone and the aluminum will look about the same as when you put it there. On the other hand, bolt the steel and aluminum sheet together, and the aluminum will rot away (and serve as a sacrificial anode to protect the steel) due to galvanic corrosion. The exception is at extreme pH. If you expose the aluminum and steel to pH extremes high enough to dissolve aluminum oxide, then the aluminum will corrode extremely quickly because it is such a reactive metal and a hard shell of aluminum oxide isn't being allowed to form to protect it. Your other point is that aluminum itself is much softer than steel, which is true. And I wouldn't use an aluminum trailer for hauling gravel or things like scrap steel regularly. But my tractor is tiny compared to most and as long as I'm not abusive by dragging implements across the deck, I would expect the all aluminum trailer to far outlast a steel trailer with a wooden deck for my use. I'm also a car guy, so there's a good chance I'll use this trailer to move a car around pretty regularly.
