Kelley,
I think primarily the reason to use interior feeders is that you know you
are feeding your own bees! Out in the open, you will be feeding all the
bees in a 3 mile radius that get wind of it. You know how much is being
taken by each colony. If a colony is weak, and not taking it either, it's
a sign to do other things. Also if the weather is bad, the bees can still
get the syrup without going 'out to dine'.
  An open feeder will also entail having floats to keep the bees from
drowning in it. Need more surface area than a bucket could provide. a
trough would be more like it. I knew of someone who did just that- cut a
water tank lengthwise, put wooden floats in it and filled. What a sight!
bees coming from everywhere!
 
Jerry Worrell, Dunkirk,MD