I would just take a nursery pot, cut it open on one side, wrap it around a branch of an azalea, then fill it with potting mix (not substrate as it may dry out too fast) and then tie the pot in place and make sure it is either supported in the air or can lie down side ways. Maybe add some sphagnum moss on top to capture some more moisture, as the roots will be in a pot that you may not water. Then wait 1.5 years. As Pitoon says, no need to take off the bark. A bit more patience is needed, but after those 1.5 years and after the worst heat of summer has passed, Then just cut off the branch just below the air layer and see how many roots it has. If it only has a few roots, maybe prune the branch/new plant.
I wouldn't wrap around plastic or tin foil. Just a normal pot with potting mix. But I have not tried these other methods. They might be superior.
If the trunk/branch element is really thick, it might need more than 1.5 years. Not sure about that. I have just tried this method on thin branches that seemed suitable for propagation. Not thicker branch sections that had ideal bonsai movement/trunk base.
A more superior option may even be to bury a branch and to layer it that way. But usually that is not practical. Especially not with specific sections that have a good shape for a future bonsai.
I am not sure if roots in a dry pot can get harmed if the plant itself can still pull up moisture from the full ground. My guess is that even if the layering pot completely dries out, in a way that would be potentially lethal if that pot was the entire root system, but in the case of a layer, the plant still has a true root system either in a pot or the full ground. So potentially, you can get away with not watering the layering pot.
Not sure if camellias are equally easy. Note that azaleas can potentially even grow air roots if they are in a very high humidity environment. Like a very high humidity greenhouse.
