Talk About Static Cling...

Mot I have the same problem with static buildup; it definitly occurs during playback as I too use Zerostat, followed by a blast of canned air for final dustoff before cueing up. Also I use a dab of Last stylus cleaner. I know that my arm is grounded & there's metal-to-metal contact from the arm base to the metal TT deck, which connects to the metal bearing carrier. I'll consider trying the direct grounding approach, but I want to verify (with an ohm-meter) that the bearing is in fact already grounded as I believe that it should be.
Really makes you wonder when you go to remove the previously-neutralized LP & the TT mat then clings directly to it, releasing with mega pops & crackles as the record is lifted away. Surprised that I don't hear static-discharge-distortion pops & crackles during the actual playback.

this is getting interesting: I've considered the insulating properties of my extremely thin "analog survival kit" mat & agree that is probably aggravating the situation. I do want to try spinning the platter for ~20 min. without the stylus engaged simply to determine the mechanism involved here. Also want to try out playback once without the mat in place (record then contacting the metal platter directly) but I do like to use the mat because it improves the sound. A conductive mat would be interesting - possibly carbon impregnated for conductivity? I'll try to research some alternatives. This is the VPI Aries platter & bearing on an HW19MK4 table. Thick & springy mats are not recommended for this rig.
Dust cover is always in the raised-hinge position during playback, but removing it altogether could be someting to try anyway.
There could be some negilgible platter-to-record slippage but I do use the 2-piece VPI delrin clamp which holds very tightly. VPI suggests applying talcum powder to the belt, so I might as well try that too. Interesting idea trying to measure the static potential (I'll use my scope which has 10 M-ohm input impedance) that should tell whether the charge is building up on the record as I highly suspect, or the platter.
Household humidity is normally 55% to 60% which should be plenty good enough.
Lots of good interaction & ideas here - sorry Mot for jumping in; I'm really not intending to hijack your thread.

OK I did some testing last night. Zaik's theory that static builds up simply via platter rotation turns out to be correct in my case - after a 20 minute spin without the stylus engaged I still get that static cling. I then neutralized with Zerostat & per my wife's suggestion I applied Endust for Electronics (an antistatic cleaner/spray) to the platter top & sides with a lint-free paper towel. After another 20 minute spin, the static was back again although the charge was not as strong as before, so at least that helps.
Measuring the spindle-to-ground resistance I get an infinite reading, so I'm going to run a separate ground wire from the bearing-carrier back to the phono stage ground. This may help despite the use of insulating mat; the spindle contacts the record's center hole tightly enough that this could theoretically do some good. Then again this grounding didn't help Mot's problem, but I'll try it anyway & cross my fingers.
Herman's suggestion regarding the static drain-brush is certainly worth trying as well; nice idea.
Zaik I must agree the cover-issue is certainly problematic; this VPI is a suspended table with the cover hinges fastened to the base which is spring-isolated from the deck, so may or may not be an issue. I'll have to experiment with sonic comparisons of cover-open, cover-removed, & cover-damped per your suggestion.
Thanks to everyone for chiming-in here with their theories & suggestions; much appreciated.