Combining several attributes with string join
The Feeds Tamper module has an implode plugin that makes this work.


  Feeds Tamper provides a small plugin architecture for Feeds to modify data before it gets saved. Several plugins are available by default and are described in the examples section below. Additional plugins can be added in separate modules or through the issue queue.
  
  
  Replace every instance of 'dog' with 'cat'
  Filter items based on keywords or vocabularies
  Make every letter uppercase, lowercase, or capitalise every first letter
  Break a comma separated list of words into Taxonomy terms or a multivalued text field
  Combine separate 'first name' and 'last name' fields into one 'name' field
  Convert urls from relative to absolute