I like the Bell Magic fine.  A buddy has one and I've paddled it.  To me it does seem to have limited capacity.  It'll will probably be fine for 3 weeks, but things might be a bit tight.

I owned an Encounter and I didn't care for it.  Too much depth/freeboard.  Really caught the wind and because it rode so high even when loaded it felt unstable.  IMHO, the Prism is a much better solo tripper especially for a moderate length trip.  Personally, I'd choose a Prism over either a Magic or Encounter.

I paddle a Sawyer Autumn Mist for tripping and I like it a lot, but I like a bit shorter boat.  I also own a wenonah Argosy which I also like.  I have not used it for a trip, but the thought has crossed my mind.  I think it would perform well.