Thanks very much,everyone.
I have the Rx upsiade down on rubberised velcro and will try to put some foam on top of the wing opposit Rx (don't have enough room to wrap Rx from both top and bottom - it is Electron 6 with connectors from the top). Will put some foam around the sides too.

Good hint about crystal falling out. I hope rubber pushing up from the wing would stop that.

Ta again