Hmmm stretched rubber bladder against pointy mylar kinda at atmospheric pressure........
There used to be a happy dozen (?) places making RC blimp bags and kits online, but I see the attraction to diy balloon. Mylar balloon bags can be had at your local party place. 3m makes all sorts of tapes available at your local building supply house. Your covering iron will seal the end as well as moms clothes iron, but use some sort of shield to prevent melty silvered mylar from sticking. Helium is available at wally world kind of places.
No,
@Mr Man there are no plans, it's kinda the point...