Surely It's not a fold down aerial you need; just a fold down mounting.
We use a standard Vtronix Raider Aerial on a modified fold down mount- see pictures.
Rgds
Nigel
www.woozle.co.uk
"There is nothing - absolutely nothing - half so much worth doing as simply messing about in boats."
Kenneth Grahame, The Wind in the Willows, 1908.