Hello Robert and Hugh,
Finding the right spot to mount your dish is not easy.
But with some simple re-inforcements you can stiffen the existing
mount. Placing a rod "triangling" the existing mount will help a lot
and does not put in much weight.
You could also try to use a pre-tensioned steelwire from a fixed
point to the pole just below the dish mounting to dampen.
Don't think that a mesh dish is a solution here. At this high
frequency the mesh should be minimum 2mm and won't be very open when
hit by a gale.
You could try a bit smaller dish, this has less surface and a wider
beamwidth, relaxing a bit on the stiffnes of the mount.
Arne van Belle