If you can adapt the EarthBox Company's automatic watering System (AWS) to your specific containers, that is the most reliable and simple way I've discovered for SWCs. I currently have 38 SWCs tended by the Earthbox AWS and I couldn't be happier. Tens of hours per week saved from manual watering - and now, I can go away for a week or more at a time and never have to worry about my SWCs running dry.
http://store.earthbox.com/AWS-Kits/products/57/
This is the best investment I have ever made for a garden accessory.
Raybo