How to prevent powdercoat peeling

I have a sensor housing that is used for winter plow trucks.  I have
my fabricator of the housing powder coat it.  It seems to have good
integrity, but some tests I have been doing with thermo-shock from
about 0 degrees F to 170 degrees F have shown some flaking problems.
The material is flaking in sheets, like the metal may not have been
prepared properly.

Can someone give me a quick prep course so that I can talk
intelligently to the powder coat supplyer?  What prep questions
should
I ask?  Are there  different types of powder coat that may be better
for the harsh environments seen by a winter plow truck?

aus.cars