A simple hot air balloon, maybe. You'd run into the same problem with a zeppelin as you're running into with the sub -- engineering isn't my specialty. I can't clap my hands and have a perfectly-working machine.

[He hums thoughtfully as he thinks aloud.] Diving... Water pressure... If we knew how deep we were trying to go, even something like ... what's it called, an atmospheric suit would work. A hard suit like that would offer room for applying crests, too. But then there's the materials problem again. Tch...