If you can vibrate loose the vibrator from the trunnion screws, you are really shaking.
I'd get some medium strength locktite thread lock and seal the trunnion screw at the top (the knurled adjustment nut) and seal the fixing screw that pushes against the lower trunnion screw. This screw is located under the vibrator arm at the base of the support yoke. You will need a very long slotted screwdriver to tighten this screw as you have to put the screwdriver through the damper and UNDER the vibrator and finally contacting the slot in the screw. Of course, you will have to remove the screw - or better yet, just back it out and apply the thread seal.
Do NOT use the permanent variety of Locktite or other thread sealant. You might want to take it apart.
Many have used plumbers putty (or electricians putty) formed in a thin "snake" and wrapped around the fixing thumb screws of the weights - you will be able to adjust them and the putty will make it not vibrate loose. If you always send with the same speed, you can set these with the removable type of thread seal like Locktite.