Kevin
many years ago I used to use a quarter wave ground plain made from piano
wire.
a bnc connector and large washer.
Drill 4 holes at quadrants in the washer. Solder 1/4 wave radials to
it, put over chassis mount BNC socket and fix with fixing nut. Solder
1/4 wave wire to centre conductor (not the bus conductor!).
It will scrunch up into a bag as it is so flexible and sits neatly on a
baggage rack.
73 de G3YXX