I'm going to combine these two parts of the hero's journey. The road of trials in the Medelia Chronicles would officially start when the Baldur and Magni come back to the camp in Northlander territory after they leave the Greenbriar Inn. In mythology, the "road" is where so much of the "fun stuff" is found. The adventures that heroes of all time have traveled are endless, of courses. The rest of Book One and the remaining five books will include one, hopefully interesting, adventure after another.
The Belly of the Whale sequence is a bit more complicated but still loads of fun. Campbell puts it this way in The Hero with a Thousand Faces - page 90. "The idea that passage of the magical threshold is a transit into a sphere of rebirth is symbolized in the worldwide womb image of the belly of the whale."
So in the retelling of the journey, there has to be a cave or some kind of an "enclosure" where the hero goes in and comes out. Inside the "womb" the hero's power's are increased and there is this symbolic re-birthing process. When the hero comes out, if the story is done right :), the hero has to fight the mythological fire breathing dragon with a "stick and a spindle." (which signifies the male and the female.) If you look back at some of the recent retelling of this journey, ( I won't reference specific movies or books :) - will let you search on your own - but some have it right and others sort of have bits and pieces of this sequence.
In the Chronicles, Charlie fights Skoll the wolf with the staff given to him by Niss. The staff, of course, has the "stick and the spindle" symbol - the spindle being where the fire is kept. Skoll, quite naturally, does turn into the mythological fire breathing dragon at the end of the battle. When Charlie exists the cave (the mother womb) his powers are greatly enhanced. He has not only gained magical powers but he leaves the cave in the "right way," meaning that his exit is in keeping with the ancient story ( fighting the fire breathing dragon with the stick and the spindle.)
So for now, I'll stop for awhile with the correlation of the story line in the Chronicles and the hero's journey. (Book One ends, of course, with the exit from the cave) What I am going to do next is to start talking about individual characters, most of which I draw from Norse Mythology. You'll love this part.