That's a great idea. I'm still trying all sorts of ways to stop the rubber tops from working themselves free.
The next thing I'm planning to try is to use a pair of blind bolts (domed head). I'll paint the domes black to match the rubbers and then drop the bolts down through the centre of the top hats, securing them from the bottom with wide washers and nyloc nuts. All you should see is a black dome capping each rubber top and holding it down firmly onto the bodywork.
That's the theory anyway!
C.