Does an rc plane tail also have airfoil or is it just flat material?
A flat piece of wood with rounded edges will work fine.  

The tail's job of producing downforce doesn't require the lift coefficients or angle of attack range required of the main wing, so the actual airfoil shape is not that important especially at low speeds, even more so under the low Reynolds numbers ("thick" air) that RC airplanes work at.

In fact most fabric light aircraft get by with what is effectively a flat surface wind deflector, like this Super Cub.