I like the idea and have made similar self-watering planters with pop bottles as another member (sorry can't remember who it was) has shown. While looking into this further on the web, I came across this plan for a self-watering planter. The video is easy to follow, although I am not sure what they refer to as "leca' but I suspect it is gravel. Here is the link:
How To Make A Self-Watering Container (DIY & Home: Gardening Basics)
Anything that will keep my bananas watered while I am out of town is welcomed.