Two main problems are a) getting through the wiring of the door pin set up and b) the 45mm gap between the metal of the door and the trim. My solutions are as follows.
Firstly, there should be wiring in the doors already. If there are speakers there, get rid of them, if not, there should be wires already. If not, you’re in trouble.
Anyway, pull the rubber boot out from the chassis to the door on the chassis side so that you can see the rubber on the chassis side. Cut a small hole in the chassis side of the boot and feed the wires through it. These wires are the ones that go from the speaker to the crossover.
Next gets a little tricky, but not too difficult. Get a multimeter and check which of the pins relate to the wires in the door already. Work out which is the negative and positive and which wire correspond to them. To do this, stick one probe in the wire clip in the door, and the other onto the pins on the harness on the door. The pin will then correspond to a wire on the other side. work out which colour it is.
When you know which one is connected (and you can peel the rubber back a bit to see the wire) strip the wire and join it with the one you pulled through before. I like to solder and heat shrink the wires together for a better job. Don’t forget to put the heat shrink on BEFORE joining the wires.
Connect up the pin plug again and it should be all good to go.
Next we’ll need to install the speaker in the door and that takes a bit of effort….