a hot air balloon with magnets inside that confine the
internal heated hydrogen protons ( plasma )
the plasma barely contact the inside of the baloon due to
magneto confinement and thus loses very little heat to
production.
radiative heat loses are minimized by a radiation
reflecting
internal coating. the plasma is relatively cold
and thus not terribly abrasive o the inside of the balloon.
in this manner you can heat the plasma through induction
and keep the balloon TOTALLY sealed. and highly
controlled internally.
obviously electromagnets can be heavy but you can use a
fusor type electroconfinement device that is light weight
and not meant to produce so much power as necessary for
the purposes of fusing the hydrogen. the goal is just to
keep it in place.
bonus point for making the sheath of the balloon
magnetically repulsed by the magnetic repulsion caused by
the plasmas magnetic field created as it moves around the
ballon, presumably around a torroidal donut shaped core
like a tokomac.