They can be placed on flat terrain anywhere except of areas immediately around enemy keeps or resources (they can be set up inside friendly keeps, on resource towers and I have seen one set up on back of second floor of inner keep one of AD southernmost castles, though I have not been able to set one up on exact same spot, but in Rayles/Warden/Glade).
As of now, any dead person of same faction may resurrect to tent no matter how far from it, unless tent is being under fire from siege engines. I am not sure about how long they last, it could be either 20 resurrections or ~20 minutes, whatever comes first. But in practice tent may be gone literally within seconds.
Tents can not be packed (could be fun especially if it was possible to pack enemy tents).