I would put a small drip of blue lock tight on the ends to keep them from ever coming loose.
althou you can not do it to the plug itseft Ray sure wishes you could after his whole sparkplug came out 2 miles up a river with no way of fixing it till he went back 2 miles to the ramp.
It is a good idea to check plug tightness after driving with new plugs a few miles.
The originals are a hard bakelite material and they do sit on plug wobbily and loose but the metal connector inside can be tightened a bit with a very small needle nose pliers to stay on the spark plug end. My opinion on this is to use modern silicone wires with rubber boots. These are better and less likely fall off or have spark jump from wire to engine block.. I also agree with Gord on checking plugs tightness after using car a couple of times. I always tighten tight and I have noticed over the years a few loosened up and you wonder "How did that happen"??? Alot of vibration and shaking going on back there in that Hemi-Amphi 43hp motor...