Layout all your parts in a clean area.
Use a sheet of tissue paper to lay your secondary mirror on face down.
Lay two toothpicks across the back of your secondary, or find some similar
thickness substitute. Toothpicks are ideal because if you are unable to pull them
out when the silicone is cured, you can just break them off! Apply a small
amount of silicone rubber on the back of your secondary and gently apply the
secondary holder on top of the silicone rubber; make sure that the secondary
attachment screw is in the holder. The toothpicks will give the proper
spacing between the mirror and the holder. This ensures that no stress is passed
through from the holder to the mirror.
The next steps are optional and at your own risk, but I find the payoffs to be worth the effort.
Again lay the secondary mirror face down on a tissue. Use the flattest black
spray paint that you can find. Holding the can at a high angle, spray once all
around the secondary. This should cover the aluminized sides of the mirror and
the silicon, preventing unwanted reflections and diffractions. Do not over
spray, this will cause the mirror to stick to the tissue on the sides.
Rather wait till it is dry and do a second coat.