The majority of compressors Ive seen have a sealed motor, so they should be ok under normal weather conditions. You just might wanna run a covered type air filter to keep the rain away. Hope this helps.
i say build whatever you can an get the stuff you need by ordering it.....the only things on my air ride i bought were the tank, compressor, lines, and bags, and switch box. Made my own 4 link made my own brackets, made my own notch. Etc etc.....if you do it mostly yourself you will have much more pride in your truck.