Don't put Vg on the threads. You whole device is an electrical ground. The body transmits the negative side of the battery up to the 510 connection at the top. If you put Vg on the threads, you could disrupt the ground.
Noalox, is recommended a lot, and it is decent. You need to work the Noalox into the threads with a old toothbrush. But the problem with Noalox, is never really solidifies. I use di-electric grease. Comes in a spray can and does solidify.
One of the problems with our mods, is they are made out of stainless steel. Really poor conductor of electricity. We would be better off if they were made out of aluminum, like a Maglite. If you have a choice, buy a brass mod. The copper in it is best conductor.
You will see mods with silver contact points, or Roduim coated springs, brass springs, etc., but the ground is still transmitted through the stainless steel body. So all those fancy bottom springs, are just a gimmick. As suggested, WD-40 is not bad, Noalox is better, and di-electric grease is best.
It is a good idea, using the polishing compound for taking the roughness off the threads. I use automotive valve seat compound. Smoothing out the threads makes for better contact between the threads, increasing the electrical ground through the body to the negative side of the battery.
Greg W.