I use a glass wine making carboy pressurized with a small air pump. The air pressure pushes the water through a humidifier float valve attached to the rim of the display. I currently run sumplees so the container sits on a stand next to the DT. The carboy holds about 7 gallons and lasts about 5 days with my current rate of evap. The glass is heavier than a plastic container, but this way there are no issues whatsoever regarding food grade plastic etc. It obviously won't fit over your sump, but with a little ingenuity you may be able to disguise it or otherwise make it look purty. Maybe a wicker container to cover the plain glass, something like that. Then you don't need to worry about access constraints in a tight location.
