Long rest should be acceptable anywhere but with a chance of encounters if the area isn't properly cleared. Also camps should be in different areas, if I am in the Underdark for instance, why would I go all the way back to my current camp to rest when there are perfectly good places to rest down there? Also, maybe something saying you are not tired enough to rest would be good to prevent doing it too often. Once the character starts saying stuff about being tired then this would be the indicator that it would be allowed.
