Not a lot of greenhouses here. A screen cage might be as close as you get. For those EMT seems to be better than PVC, just because of the expansion and drooping problem. The install is usually bend up the pipe, paint it to match and install it. Cosmetics may not be an issue if this is a commercial greenhouse. The issue might be direct water spray from irrigation.
RMC might be better but the cost will be prohibitive for most customers
