You can put the feather duster anywhere you feel it will look good! I have put three between the rocks and one is on the bottom & doing well. Check out your LFS & see where they put them. Don't hesitate to ask, ask, ask! They are filter feeders and shouldn't require too much attention, but there is food you can squirt in their vicinity.
I have a couple of feather dusters in my crushed coral. I just took my finger, made a very shallow trench, placed the tube body in it, covered it over, and VIOLA !!! They are very happy. They are filter feeders and do not require a lot of attention. I have oter corals and I use ZOE and strontium, and the feather dusters are loving it. I would also mention that they should be in at least a medium water flow.