I hate ruined trips! Your entire post sounds intelligent IMHO from start to end.
Perhaps fill the wound with NON asphalt based undercoating then screw or rivet a piece of 20 gauge over top, then when that's done, coat the repair with even more undercoating?
When comparing trailer springs I always used to verify the new spring had a thicker main leaf than the original. Caught too many higher rated springs using the same thickness main but merely adding more leaves. just a thought...
May future trips be brighter and trouble free. You paid your dues IMO.
