Need Advice, Power Wire through Firewall?

For those of you who have poked a hole through the large rubber grommet surrounding the wire harness, did you use anything to seal around the new wire on the engine compartment side to keep it waterproof ? I'm thinking silicone or RTV sealant ?

I am also considering using a pencil tip soldering iron to burn a hole through the grommet rather than poking a hole with a sharp object, maybe that will prevent future tearing ?
 
It's rubber, so it might smolder and smell.
I used an xacto knife to make a big X. It's thick rubber and unlikely to tear.

I think RTV would be ok, but the location of the grommet is well protected. It's high and away from the wheel wells.
 
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