Firstly, your campaign sounds epic, hope it goes well!
Secondly, thanks for taking the time to share your play report. I wish more people did that.
I’ve also found Rotfang can go down fast if the weak point is hit, but I don’t mind, I think crafty PCs should be rewarded. I'm glad you chose to bring the troll in early; the module works best when the GM adapts on the fly based on whats happening as appose to just relying on the tables.
Some hunts ive run do turn out a lot easier than others. But on the flip side ive had some turn out pretty brutal. I do find though that’s Mörk Borg for you, with creative players (and Omens), the system can sometimes be surprisingly forgiving. If things feel too easy, don’t be afraid to toss in something wild, maybe Rotfang has a mate nearby?
As for the cart scene, I like to have trolls run before hitting half HP to be honest. Keeps the action moving and ramps up the chaos.
My advise for future hunts is to always favour what seems cool over what the table is telling you. The tables are best used to guide your hand.
The Shadow creeper may set your PC's "troll fears" straight again. You can make the encounter pretty harrowing for the players.