... Looks like the ZS6BKW may be the way to go, unless I build my own.
Building your own is fairly easy.But be aware of expectations: the ZS6BKW was
designed to have a low SWR on 40, 20, 17, 12,
and 10m, suitable for coax feed. On other bands,
the SWR will be high, and losses can be significant,
either in the coax, the tuner, or both.
You can reduce feedline losses by running balanced
line all the way to the tuner, rather than using
coax. In that case, the exact lengths of the antenna
and the feedline really don’t matter much - it is
just a doublet of whatever length is convenient.
(80m efficiency will drop as the antenna is made
shorter, however.)
That’s not to say it is a bad antenna, just that
those advertising it as an “all-band” solution are
perhaps being overly optimistic if efficiency is
an important consideration.