Premier uses Stainless Steel, grade 304 for the entire housing of their evaporative coolers . This type housing is a virtual lifetime use medium. Galvanized steel whether or not painted, has a very limited useful life span. Painted plain steel is also very limited in useful life span. Fiberglass is a good substitute but cost is prohibitive and dimensional instability can occur.
Outside surface is often irregular.
The only sensible housing medium is Stainless Steel, grade 304. It is commonly used in kitchen equipment including the kitchen sink and the cost is usually about equal to the other metal finishes. Premier uses only Rigid Media for its' cooling medium. Average useful life is 2 to 3 years without changeout under normal operating conditions. It meets the requirements of UL900.