After seeing the great stuff some of the others have built, I'm slightly embarrassed to continue with my rather half-assed attempt, but I'll try to finish anyway.
I've added strips of cardstock over the leafcatcher bit (no in progress pictures), just picture some tapered oval shapes and you'll get the idea.
The balloon will need a cap
And something to mask the bottom where the strips meet and smooth the transition to the central shaft
The 'finished' build
The paper strips could fit (quite a lot) better (less 'gap' showing) but I won't redo them. I really have no need for a balloon, and still have a lot of figures to finish so I rather spend my time painting those or building stuff that might have a chance of being used.
I will try to paint and base the balloon, just to have a finished entry. My idea was better than the execution, but I'm convinced that with spending a bit of more time someone more experienced/talented could really make an excellent balloon this way.
Gathering materials and supplies: 25 min
Plans/mock-ups: 10 min
Building: 3 h 45 min
Pictures/LAF post: 45 min