I'm not sure if it's given the climate down here is more brutal given termites, wet conditions, hot conditions and such, but I prefer to soak the wood for the boxes in a copper based preservative (Copper-tox). Apply a coat of indoor/outdoor latex primer on the outside and over that apply a layer of exterior semi-gloss( given I have a gallon just laying around from that last home improvement project; same deal with the primer). The boxes seem to hold up very well with this treatment.