What are your concerns about installing gas turbines outdoors without protection other than from the obvious issues?
I can tell you that acoustical enclosures are unnecessary as long as the noise will not pose a problem for anyone or anything in the environment.(Gas turbines are extremely noisy)However a weather-proof enclosure would be extremely beneficial for many reasons.
I can also tell you that weather and the operating environment of an open air engine will greatly increase maintenance costs and reduce the reliability of the engines.
Also if you are planning on installing any type of large frame gas turbine, operating issues and warranty claims will be your prime concern. Today's large frame engines require specifically designed insulation, heating and cooling schemes to maintain operating tolerances which, if not closely monitored, will tear an engine up in a matter of minutes. Rain, direct sunlight, and extremely cold environments will greatly affect performance not to mention the instrumentation and electrical issues.
I can also tell you that I have met customers of large frame engines that have lived to regret the fact that they balked at the cost of a weather-proof enclosure. I will also add that as a Technical Director I hated working on open air engines.
Hope this helps
Romefu12