@ Urbicande
Of all the troll assembled I could see sleipnope jumping above it and confronting the group directly.
Either that or he bullies his minions into going forth into the flames - and then you have flaming trolls. Just as bothersome as their internet counterparts.
Sleipnope is a ghost, though, so I'd expect them to just walk through the flames unaffected.
My guess on defense is that the Cattank's spotlights swivel to the sides and headlights on. The light might keep things at bay on those three sides. That leaves the back to be defended. If it's tough enough it might be able to keep the trolls out. Ghosts...well...that's going to be Lalli and Reynir's job, and with any luck they can get in touch with Onni.