My Vandas and Cattleyas seem to do fine outdoors. I think about protection when temps drop below 40F. We rarely have frost, I usually just wrap my racks in tarps. If really cold I put a string of Christmas lights under the tarp below the plants. This past winter we had lows 34-37F. The temp under the tarp without lights was 3-4 degrees F higher. All of my Vandas and Cattleyas came through without a problem, but I did have damage to some dendrobiums and some phals. The parentage of every hybrid probably makes a significant difference in cold tolerance, as does conditioning and watering before the cold.
If I was right about your weather being similar to ours, Martin Motes book on growing Vandas in Florida Month by Month would probably be pretty applicable (obviously the months would be flipped), although the chemicals he discusses may not be available under the same name there.
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