Such a low relative humidity is difficult to deal with. It must be hard on your own skin and mucus membranes! Have you considered getting a humidifier for your home? They can be connected to furnaces and central AC units.
Another way to raise the humidity is to keep the chameleon in a small room with the door closed, and keep a small humidifier, a fish tank (or other open water), live plants etc in the same room. I was suprised what a difference it made when I started keeping my hermit crabs (which have a moist substrate) in the same room as the chameleons.
You might like to look into having a dripper or auto mister running all day (dealing with the subsequent run-off /build-up of water may be a problem without a drainage system)
You dont have to remove the coconut fiber substrate. At the moment it may be needed for humidity reasons. But you will need to be careful about clean up (bacteria growth, fungus, fecal matter eaten by stray feeder insects which are then eaten by chameleons). Also if your chameleon shows an interest in eating the substrate or if prey is lose and eating that prey could result in coco fiber sticking to the chameleons tongue, you risk impaction issues.