Clean the areas real good with Dawn, hot water and a sponge. Once the crud is removed go over it with some Simple Green and a tag or towel. The surface should be clean and dry before applying the RTV silicone.
I squeezed out the silicone in a bead and went back over it with an old tooth brush - ya know, a freebie from the Dentist... spreading it out and creating some peaks/valleys in the silicone. Rolled out the nomex, cut to fit at the end, pressed it down with my fingers all of the way around, then wiped away any excess silicone (just a few places).