What is done at Fruits and Exotics is to build a frame work about them. I decided to do something similar for 3 small citrus trees of 3-7 fet tall. In late November When Our first frost starts I surround the frame work with plastic sheeting on three sides. The forth side is maintained as an open flap and does not get dropped until the temperatures are likely to go below 26 F for 5 hours or more. When that happens I drop the flap and secure that side with weighted objects. Inside I run a small spray of water to release some heat. It worked last year and I will do for the comming year winter also. The frame must be sturdy enough to withstand a strong winter storm wind. I also cover the base of the tree and the lower area of the graft with mulch.

Not sure what you are saying as I live in the Houston area and I do not put up any protection for my citrus trees unless we are going to get a heavy freeze.