Gently try popping the speaker grills off. If you feel resistance, you'll have to remove the entire door panel.
I suggest using a SPST (or SPDT) 30-amp relay to run your neons with a switch.
2-way switch (non-lighted):
Terminal 1 to 12V fused from battery
Terminal 2 to terminal 86 of relay
Terminal 30: 12V fused from battery
Terminal 85: ground
Terminal 86: from switch
Terminal 87: to positive of neons
Terminal 87a (only on SPDT): NO CONNECT
This way, you'll have manual control of turning on/off the neons. However, if you want the neons to turn off whenever the car is off, connect Terminal 1 to ignition or accessory.