The collapsible 4 position (plastic) stock went on the CAR project this morning. Now I already want to take out some of the rattle and lateral movement. The first idea that came to mind is gluing plastic shims to the buffer tube that will remain hidden in both the extended and collapsed positions. If you've been down this road before, what ideas have worked?  

GunCat...I replaced my Bushy buttstock with one from CMMG. The stock they sent me was what I expected to get from the GO! I kept the Bushmaster extension/buffer ass'm & only replaced the buttstock(fiberlite 4pos). It worked like stink & cost very little...Bud

Get a RRA new style tele stock (these don't rattle at all)

They are tight enough to mark the buffer tube on four sides.

GunCat,

Get a spray can of
Plasti Dip
Spray-on
Heavy Duty Flexible Rubber Coating in Black.

Pull the butt stock off by pulling down on the lever and pulling the butt stock off the back of the tube.
Tape the extension retaining nut forward(plastic bag works), and shoot the receiver extension with a coat of rubber.  Most of the time, a single cost is all that is needed.

Also, remember to clean off the oil on the tube before you spray.

If I recall correctly, there was a post a couple of months back about using some plastic shims glued to the bottom of the tube.  Perhaps you can do a search for it and find it.