Have you tried the Christmas lights trick? String Christmas lights on your fruit trees. If using the LED kind hang them a little more thickly than with the incandescent kind, but the heat they emit is usually just enough to keep frost off the flowers.
No we haven’t. We only have enough for a little 2 ft. tree.
We did use one of those metal lights with a hanger and 100 watt bulb 2015 spring, and put a sheet over the tree - that was when it was smaller.