I just have a cheap AR electric pressure washer but I do try to use pump saver on it before it freezes as part of my winterize routine. I use AR North America Pressure Washer Pump Saver. I basically run the power washer after draining what I can and pour enough to get the fluid to exit the machine. My first cheapo pressure washer lasted 8 years with light duty (just yearly power washing house, maybe pressure wash driveway and sidewalks every 2-3 years, wash cars 2-3 a year).
I keep it in the attached garage where it gets cold but doesn't get terribly cold (I have soda cans and they've never burst in a cold snap like when I grew up in IA, but I'm just in MD). Maybe it gets into the teens for a few days in Februrary. I did have a cold snap one year where it got into low single digits where one section of my kitchen cold water pipe froze.
I've not tried to keep it in a detached shed in the winter season, but I would expect more risk.
Not sure how the pump saver would fair on a gas powered power washer, but perhaps it is worth considering. It's at least better than nothing.