Gary, when I used antifreeze, I mounted a 5 gallon tank to the wall. Then I ran a hose from the bucket to the inlet of the PW. I ran the PW until antifreeze came out the gun, then shut everything down. When I started the next job, I closed the antifreeze tank valve and ran the pump until water came out the gun. I never tested the antifreeze. When the antifreeze started to slush, I dumped the solution into another bucket and dumped the slush out. The antifreeze went back into the solution bucket, with a gallon added as needed.
I got tired of messing with antifreeze and put drains on the tank and pw. I drained the tank, pw and hoses. I installed a valve at a high point and added a tee and Type D quick connect. Then when I ran a hose from the N tank to the high point and blew the water out.
I got tired of that and installed a propane heater with 2 of 10 gallon tanks on the tongue. That worked so well, I added a 12V fan running off a battery to move the warm air in the trailer. Next I added a battery charger to keep the auxilliary battery charged. At the shop, I run an extension cord to the trailer for the battery. I also added a freezer temp gauge to monitor the temp inside the trailer. On my list is to add a solar charger to the roof so the battery will charge in the daytime. I will also have my mechanic install an isolater to charge my battery when the tow van is connected.
Alexy uses concrete curing blankets to keep his stuff warm.
There are lots of ways to keep the pw from freezing.