Hi Greg,
I understand that teaching your son to drive is a somewhat daunting prospect given his propensity to back into parts of your house. I'm currently on my green P's so I can tell you all the mistakes my parents made
In truth, my Dad was an excellent instructor, despite my arguing occasionally - being a 16 year old I knew so much! The key is, as many others have said, you need to show confidence. If you are appearing nervous, worried, get angry, or use your imaginary passenger brake (as my Mum did) you're only going to make him hate driving and get worked up. The best thing you can do is remain calm, despite how crazy your son may be driving, he needs to see that you are there to help him. You say you live out west, I'm guessing a decent ways out? Try and find a quiet town, with wide roads that he can practice. Don't take him down small, narrow roads - as my Mum found out on my first time out with her and a guy came over a crest at 80kph and just about killed me day 1 of driving luckily I got out of the way just in time (I was doing like 40kph made it easier).
Start in areas of town that have around 50kph as the limit, and he doesn't have to worry about much but keeping it between the lines. Then build up, maybe let him drive on a main road with maybe 60 as the limit. Then build up to 80 zones and freeways, and finally those goat track 100 zones between country towns. You need to build up step by step. I learned to drive in my Dad's old, very well travelled VT Exec, no driver assists and I learnt how to park really well and unlike my Mum and Dad, I haven't backed into anything.
As for the instructor lessons, yeah they're fine, but spread them out through the hours. Take him driving for say 15/20 hours, then throw a lesson in. If you're driving an hour to get to the instructors place, there's no reason he can't start driving that when he gets the skill and confidence.
Again, the key is for you as the adult to remain calm and in control, don't get angry because he can't do something properly. Every mistake we make as drivers, everytime we almost have a prang, everytime we bascially #### up - we get experience. And remember, he is very unlikely to back into your mailbox again, you need to teach him to learn from mistakes and that it's OKAY when he does, and that it's just a means of learning.
Mike.