Waterproof enclosure is commonly used in outdoor environment. Empress 2.4GHz active reader is very easy to mount on any waterproof enclosure. Here are some tips,
1) Mark the holes on the metal plate and drill them
2) The controller (if possible) may use 5V and share the DC inputs with Empress Reader when applicable.
3) Mark the antenna polarization on antenna and also outside the box for easier maintenance
4) Use cable glands for external power input and data out
5) This setup also protects the antenna inside the box, you may also try external directional antenna for easier tuning if necessary.