You want this?

#!/usr/bin/perl --
use strict; use warnings;
use YAML qw/ Load Dump /;
use Data::Dump qw/ dd /;
my $it = {
  Things => [
    {
      Name => "thing_1",
      Sub  => {
                key1 => "value1",
                key2 => "very very very very very very very very very 
+very very very very very long line\nwrapped value2",
                key3 => "value3",
              },
    },
  ],
};
dd( Dump( $it ) );
print Dump( $it ), "\n";
__END__
"---\nThings:\n  - Name: thing_1\n    Sub:\n      key1: value1\n      
+key2: |-\n        very very very very very very very very very very v
+ery very very very long line\n        wrapped value2\n      key3: val
+ue3\n"
---
Things:
  - Name: thing_1
    Sub:
      key1: value1
      key2: |-
        very very very very very very very very very very very very ve
+ry very long line
        wrapped value2
      key3: value3
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