Using magical items like that in the Underdark could go wrong though... that just as an aside.
I'd say: Relegate long rests to overworld maps and save areas... like Dragon Age Origins did it. If it has to be "rest anywhere", though, then either give a long rest option without the full camp (just sleeping, no extended functionality), or create a handful of camp layouts (overworld, dungeon, underdark), or go with the aforementioned magic options, but best link these to some expandable resource, like spell components, magic item charges, etc.
