I really don't know too much about Carbon Piles, but thanks...I will check into them.
The reason that the variacs need to be that thin is simply a space constraint that I am working with.
I am building a panel consisting of 8 variacs. As it currently stands the panel is 2'x3'. The maximum current is to be approximately 5-7 amps through any single variac. Does anyone know where to find variacs that are smaller than 5"x5"x3" capable of handling this current?