If you haven't already, I'd take it for a test flight before siliconing it into place. It'd be okay if it ran hot on the rock - thermostat to regulate the temps - but if it didn't get hot enough you'd need to unstick it.
Just my 2 cents. Good luck
^^ yeah sorry if there was confusion.
That's what I did mean. Run it with the slate on first for a gauge on temperature. Might find the slate to be too thick and not transferring enough heat? Just a test run before sticking it down might save having to clean off cured silicone