If looks are not that important, then a simple gravity feed ATO would be easy to set up with parts you may already have. All you need is a container fitted with a spout or valve at the bottom, some tubing (flex and rigid air line) and a mechanical float valve (furnace humidifier float valve works well).
I have a similar set up although it's not gravity feed since the ATO container I use is a bit large to set up above my display, so it's beside it instead. I use a small air pump on a digital timer to pressurize the container. The air pressure pushes the water out of the container into the display through the aforementioned mechanical float valve. For this you need a container that can be made air tight with a stopper which needs to have two holes, one for a short tube (air in) and a long tube (water out). Other than that, I have a small check valve between the air pump and the container to guard against possible back flow. I also had to DIY a bracket to hold the mechanical float valve. Pics follow.
Glass wine carboy (about 7 US gals)
Float valve
