I cover my satsumas, kumquat, grapefruit trees and use space heaters with thermocubes under each plastic cover whenever it's supposed to get down to 32 degrees , because my trees have fruit on them all winter long, and a freeze here can last for days, and it can easily be 10 degrees colder or warmer on top of this mountain than it may be down in Asheville, NC. Like you, I've put too much time, money, love into my citrus over the years to lose them over a single weather event. Citranges and poncyrus, yeah, no worries, they can take it, but real citrus don't like freeze. I think your smart to protect your valuable trees. Good for you.