I am finishing the wiring on a 20x24' addition (completely enclosed & insulated) to the rear of an open garage, which will include three exterior/outer 20a receptacles (two in the rear, one on the side). I understand I have to use GFCI plugs and weatherproof "in-use" covers, but any special requirements for the receptacle boxes themselves? Can I still use the standard plastic/PVC style boxes?