[David]

Aaron, the air in Kl is indeed drier and hotter as compared to Johor. I can feel the difference as I do travel outstation. On top of that Johor has more belukar and greens.

Ken,

The water trays do increase humidity a little. Since your plants are placed in the balcony of your apartment you cannot use shade cloth. Your management won't allow that. Shade cloth actually helps increase humidity within the area it covers.

The only other thing I can think of is for you to place more plants in your balcony among your nepenthes. Put them all close together. Water evaporates from the leaves of plants too and that will increase humidity. Also your neps will get dappled sunlight. Then your problem with scorched leaves will be solved.