I would put 2 ac units in the roof, and a Fantastic Fan in the center. Just leave the fan open, and you have ventilation. I doubt a single AC unit will provide much cooling for a 26 foot trailer with that much heat rejection of cooling units and heat lamps inside.
Another idea is a pair of portable AC units, with dual hoses. Cut small holes in the outside wall for air in and out for the cooling unit. I would get the ones that evaporate the condensate in the exhaust stream - no buckets to drain.
As for heating, I would mount infrared lights above where people work.
