OK. Here's my tube version. Two slabs of 2lbs per cubic foot closed cell EVA foam, with gray on bottom and orange on top. You can spot it from a half river away. The two slabs are glued together. A drinking straw is buried in the foam. A hook lashed below. A little nylon mesh reinforces the thorax area.
You could peg this to the leader. But I haven't found right sized pegs yet. I need to get some tube fly tubes.
But you can also thread the leader through the tube, back over top and around the thorax once or twice, and then back through the tube again (the leader does NOT go through the eye of the hook).
That fastens the hopper well enough you can actually catch a fish. And they will bite it EVEN when mounted in the butt section of the leader. You can loosen it up and move it to any point on the leader. It does not kink the leader. You do have to be careful with this rig. I hooked one on a branch last summer and broke my rod tip, because the hopper was at the 30lb part of the leader instead of the 6lb part.
This floats so well you could use it as a strike indicator (a bobber) for a small Mepps Spinner. Not that I would ever do such a thing, you understand. ;=))
I like AlanB's too. Better in fact. His is far more handsome. But this baby got the flotation. And a hook.