question about metal corrosion for a possible repair

sprinklerman thanks for the advice- I got a 50 ft roll of this for about $50 on ebay and it's 3 times what I need, so extra for future jobs. Perfect thickness

Check with a dealer. Those pieces are available. I had to replace one on the Cougar after a little accident. It was reasonable cost, already shaped to the correct curve and painted white. Just had to trim to length.

Coil stock at Home Depot or your local siding distributor . Its Aluminum

I buy aluminum sheets, panels, and structural pieces at Discount Steel. They are local to me so I visit the yard and try to buy off cuts from the fab shop by the pound.
They do ship and have a fairly complete inventory. Custom cutting is also available and reasonable.

An alternative might be a metal fabrication shop in your own area or a siding contractor if you can use lighter gauge material. Do you know, offhand what gauge you need? I do have some sheet goods here, even vinyl coated.

I want to stick with the original look, too much diamondplate on a trailer looks odd. I can use a metal pipe to curl the underside like it was, I just dont want corrosion issues down the road

How about aluminum diamond plate.

The aluminum siding above is probably going to chalk and leave streaks on anything below it. If you paint the galvanized it will probably not show any chalking streaks. You may consider getting aluminum sheets of up to about 12-foot long and 1/4-inch thick, but you'll have to go directly to a supplier to get it, you won't find it in a big box store; and that will probably have to be painted also. I don't think you will have any problems will galvanized metal below if it's painted, depending on how its attached to the aluminum above. Piercing the galvanized coating all bets are off.