One of the mods I did to my own VPI 16.5 was to replace the Mat. I also had a custom made acrylic platter made too, but that is not pertinent to your question here for the time being.
I replaced the cork mat with a 1/8" thick Neoprene Rubber Mat, of Shore Hardness of 60 I believe. Probably a Shore Hardness of 40-80 would be fine.
Supply houses such as McMaster Carr carry such. I first tried a self adhesive backed sheet, and had some issues with minor bubbling which I wasn't happy with, so instead acquired some sheeting with no adhesive, and permanently bonded the sheet to the platter with DAP Contact Cement.
McMaster Carr will sell 12"x12" sheets, and this is all you really need. First the Spindle Hole was punched, then smartly also punched the 3 Holes for Platter-Arbor Retaining Screws, thus won't ever be a need to remove the Mat from the Platter.
The black Neoprene is easy to clean, waterproof and chemical resistant, easy to see any dusts that might settle on the Mat, the Mat material is soft enough that there would never be any damage created to the record, and such will last a lifetime.
The Cork Mat on the other hand will eventually get dirty and old, and if like many, you're using some additional Mat for the flip side, this is extra work IMO.
My own machine can be seen at Osage Audio's site, under RCM Museum. Mine's the first machine on that page.
I also added a small AC pancake cooling fan as well to the rear of the machine. Yes, a little bit of work, but the machine runs absolutlely cool, no matter how many records are cleaned.
Mark
