Hole in firewall for amp/electronics install?

I know several of you have installed amps and other things in your cars, what I'm wondering is where is the hole in the firewall? I know there typically is, or did you all have to drill your own holes to power your amps?

So in other words, where did you run the wiring to power your amps? Im not interested in an amp, right now im wanting to mount and hardwire a power inverter in the car somewhere.
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I have a 98 and drilled my own hole below the glove box. I have a clear shot right to the battery. I pulled back the carpet, drilled, and sealed with silicon. Plus, if your doing an inverter a nice place to mount it would be under the glove box, plenty of room.

I was actually thinking about mounting one inside the glove box, or in the compartment below the radio or somewhere around in that general area.

I guess I can just drill my own, how hard was it to drill through? Is it pretty thick?

No it wasn't bad at all, it took probably 10 minutes total from removing carpet and replacing.