recommended outdoor enclosures

I'm in need of my first free-standing, pad-mounted outdoor enclosure, 19" rack rails, 12-18 rack units, with about 400W of heat load inside, for use in the Massachusetts climate. What do people recommend as far as contruction, cooling/heating options, NEMA ratings, security options, etc. for this use? I was hoping to keep the inside temperature between 50 and 85 degrees Fahrenheit, although my worst-case components are rated for 41 to 104 F (4 - 40 C). If a full mechanical A/C system can be avoided, even better. A thermo-electric cooler would be nice. Thanks.