Frost blankets might work. Mine will keep the temp up to 8 degrees warmer than the outside temp.
The plants are in much more danger if it has become real cold real fast. If the temp has been gradually dropping they can withstand lower temps than a rapid decrease because they have slowly become accustomed to it.
28 is really pushing it especially if there is wind.. Really. From my understanding and research that will likely hurt or kill them unless they are protected some way.
