How difficult is it to remove (and replace

) the A pillar trim and the side panel that is mentioned.
This is my first Holden in more than a decade so I'm not familiar with all the models and variations but on mine it's not difficult at all.
There's no screws attaching so just pull from the top and gently ease it off.
Don't just yank it off as there's airbag and tweeter wiring attached to it.
I didn't disconnect the wiring off the trim as old mate in the video did. There's plenty of room to feed the cable down behind it and into the area behind glovebox (which is where you'll find the doc connector).
edit: Here's my condensed install version from another thread
Remove glovebox
Install dashcam
Hide cabling behind roof lining
Pop out passenger side A Pilllar cover (no screw on mine, just pull from the top first - be wary of airbag wiring)
Run cable down behind airbag apparatus into area behind glovebox
Find DOC connector (easy to find, it's the only one there)
On mine there are only 3 (or maybe 4) pins inc Earth, Acc, 12v constant.
Work out which is which with test light or multimeter
I bought the powerbox as well so the dashcam male end (to power) inserts into the powerbox female socket which in turn is connected to the DOC socket.
I used these http://tinyurl.com/hu5xa9g to connect socket wires to DOC socket pins (just need to spread them a little). I'm a bit old fashioned so I soldered cable end into the blade terminals. I connected the earth wire to a bolt in the area.
edit: Forgot to mention that I stuck the powerbox (Vicovation Power Plus) in the back corner of the glovebox and because of the connector position didn't need to drill a hole, just fed the wires up beside the glovebox and over the side wall.
I wrapped power male/female + extra cabling in some foam and cable tied out of the way - there's plenty of room in there.
Test, put everything back together, enjoy.