I never check the CPU when using Kneadable eraser. If I have a good CPU, it stays like that for month and months, until, I upgrade or want to switch CPU's. And I never use vaseline in the socket. You could, it won't hurt anything, just a little messy when kneadable eraser comes in contact with vaseline, it makes things a gooey mess. DON'T mix eraser and vaseline! Try to keep them separate, especially around the socket. I use Vaseline to coat the entire surface of the board, then melt with heat gun. I use eraser around the socket (completely covers it), then pack in toilet paper between where the eraser stops and the mosfets, Vr's begin. The TP is my separation of eraser and vaseline.
If you completely cover the socket with eraser (only the flat surface of the cpu should be visible), then no moisture can get in, period.
Oh, and eraser is not insulation, so it will frost over too. Cover it with a gasket made from a blue shop paper towel to absorb any frost/melt that will occur after you are done benching.
Put blue shop towel gasket on top of eraser:
The put a foam insulation gasket on top of the blue shop towel:
That's the basic idea anyway