Replacing a single panel is not difficult. The difficult part is that the panels are 50" wide. Standard aluminum is only 48" wide. thus you do not get the overlap to be water tight.
Contact the local distributer of the brand of trailer you are buying, and order a piece of 50 inch aluminum. Or you can source the aluminum from a local supplier and double layer the section. Over the years I have fixed lots of trailers this way
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