Another more indirect way to deal with the problem could be to make resting a less optimal choice than it currently is.
For instance, a system that recognize if the player takes a rest in between skirmishes in an area occupied with multiple enemies belonging to one faction. This could trigger reinforcements, enemies in more advantageous positions and/or alarms & traps, making the next combat harder and more likely to require resources. Reward xp for extra enemies, but take this from other xp rewards so it does not get exploited into an xp farming tactic. Added advantage of this would be *IMMERCHION* as it makes the NPC behave in a more believable intelligent manner.
