Some sort of balloon would work, but maybe not something as substantial as a Zeppelin. We've sent balloons to >100,000 ft here on Earth, and in general a balloon that makes it to 100,000 ft here should float easy at the datum on Mars. Same pressure, and since CO2 is denser than N2/O2 a helium fill would give even more boyancy there than here.

On the other hand, the balloons we send to such high altitudes have a far higher volume:mass ratio than a Zeppelin or blimp -- huge plastic bags with a tiny instrument capsule hanging beneath them, no engines. I'd imagine you might get away with something having a very light rigid frame -- composites, maybe -- and very small motors, but not a floating cruise ship like the GZ or Hindenburg.