I am a field mechanic all year long. You might think that after a rain when it is too wet to work in the field I might be inside the shop. It doesn't really work that way.
When tractors are parked it is the best opportunity for preventative maintenance and they are only parked here when weather stops work.
The growers here know that there is a brief window when the weather stops field work so annual inspections and tune ups have to be done in the mud, fog, cold and rain. My phone starts ringing at the first sign of rain.
Any part that is bare must be sprayed with WD-40 quickly to prevent rust. Many parts suppliers use large heavy duty zip lock bags for parts which I always save. They can be used to protect parts and hardware while things are torn down. I keep blue lint free rolls of towels to wipe parts dry and my nose when it runs in the cold. I wear nitrile gloves to keep my hands dry and parts clean. Most important is rain gear because mud can easily be blown off with an air compressor.
With preparation you can work in these conditions comfortably and you have a good excuse to go mud boggin'. You can fling mud all over a company truck and the boss doesn't get mad. You had to get to the tractor, right!