Scan through our Index of Key Forum Threads for a number of kiln/flue-curing chamber approaches. My kiln is made from 2" XPS foam (extruded polystyrene) insulation board, and functions as a kiln most of the year, and as a flue-cure chamber for 6 weeks of July/August during the growing season--if I'm growing flue-cure varieties that year. It cruises at ~128°F for kilning, and handles up to 165°F peak for flue-curing. The circulation fan must be engineered for a high-humidity environment (e.g. a bathroom exhaust fan). Seams and door seals are important.
Multiple air-cured varieties inside the kiln at the same time do not flavor one another. By contrast, if you kiln anything that has been exposed to smoke, it will impart a smoky character to any other leaves within the kiln.
Bob