There are a large number of edge molding profiles available and changing to a trim with a narrow edge that will show and a wide edge that will allow you to drill into the metal framing would probably be best.
The Teardrop Trailer Supply stores have a really good selections.
Personally, I would go to a trim that comes up the side at least 3/4" and preferably 1" and slightly curved to allow applying sealant to keep water from causing anymore rot to the plywood backing to the exterior skin.
There are some that have countersunk holes to allow the use of oval head screws and it is not too bad looking. To me function over form would be best.
