If you use the above formica with teflon, preferably virgin teflon, you will have a good working scope. Those plastic pads used by some do not provide the same "feel", and should be avoided since it does not cost that much to use teflon.
A teflon pad under the center of the rocker box will decrease the stability if its contact surface is above the plane of contact of the three other pads. Even in 24" Dob's, there is no real need to elevate the center, if properly engineered. I also recommend a bushing or bearing be installed in the bottom of the rocker box for the bolt to slip through. This allows all of the effort that you apply when moving the telescope to be translated uniformly.
Chuck Dethloff Forest Grove, Oregon