The best place to park is the rugby club.
Access is either by walking past the rugby pitches and on into the woods or walking down the private road that was part of the Pollok Estate and then heading into the woods at the roundabout before the big house (which seems to be called Pollok Castle).
The trees block access to the GPS satellites so it can be difficult to get a fix.
The cache is at the far end of the woods near a small stream before the open ground, which I think is farmland.
Obviously, there is no need to go anywhere the motorway.