Is inlet to the barrel in the bottom or top fill?
 
My filter has the plumbing going into the bottom, up through a few Malta Mats, and then through a mass of roots from the Hyacinth.  The water is crystal clear.  I have seen filters that are bascially gravity feed, and they work great.  I think it comes down to personal preference and aesthics.  And in your case space is an issue.