The foil treatment really does work to keep temps and humidity up, but, as a suggestion, you might get even better humidity if you raised your lamp up to hang (or clamp onto a nearby shelf or something) about 8" or so above the lid. I found that once I raised my lamps, the humidity didn't drop nearly as fast. And, with the lamps raised you can place a damp washcloth or paper towel over most of the 'hole' to increase humidity further.

Just my worth of experience.