I've been trying to place a couple of dead skeletons, much like the dead messenger in the Trail of the Serpent in the Pale Pass quest. I need the skeleton to remain connected, and to pose it lying on the ground. The Dead Skeleton creature falls apart when Havok is turned on, and seems to hover above ground level instead of falling completely. Is there another skeleton creature that doesn't fall apart that I should be using, and do I need a collision box below the ground to avoid it falling through when I try and pose it? My attempts with Ctrl+Alt have so far resulted in it falling through the ground every time.

I haven't had this problem with dead bandits, for example, just skeletons.

IIRC the skeleton has been set up to fall apart ondeath - and looking at pale pass they actually have 2 skeletons placed which are set to opposite enable states through parenting so that they can have them go from dead to living by enabling the live skeleton. In order to actually place a full skeleton and arrange it you might try creating a skeleton armor by importing the pieces into a single NIF and creating a full body armor that uses all slots (set as unplayable) and then create an NPC that wears the armor - So that the game just thinks it is a regular NPC wearing a specific armor and you can then arrange him like you do a normal dead body.

I'd have expected there to be a skeleton in the CS without the "fall apart on death" option for this already, but I haven't found it. All the dead skeletons that are lying intact in the game seem to be the regular variety. The one I was referring to is not at the Pale Pass fort, but the is the messenger you find in the cave on the way there (with the orders next to his hand) - he's never live.

I need to make myself a skeleton with horns on the skull (and hooves) so I may well create the regular one I need on the way to that.