Cecil, W5DXP wrote:
"The only way to improve on that on 75m would be to mount a piece of
sheet metal on fiberglas poles connected at ythe ends of both bumpers."

Kraus gives some support to that idea. Cecil has the 3rd edition of
"Antennas" In that edition, there is a "Disc antenna" on page 720 with
some similarity to cecil`s suggestion.

The "flush-disk" antenna, (d) in Figure 21-11 is said to be comparable
to a 1/4-wave vertical in performance, but has no projection. It could
be covered with a dielectric sheet, make no noise in the wind, and break
out no fluorescent tubes in parking garages. But, at 75m, the 0.3 lambda
dia. depression to contain it would measure 22.5 meters. That woud
require a vehicle that was very large indeed. At VHF and UHF it could be
very practical.

Best regards, Richard Harrison, KB5WZI