I live in Wisconsin, but my MPCNC has been indoors in relatively constant temperatures and humidity. I do have some 3D printed parts in PLA on a snowmobile that has been out in the elements over the past year and I haven’t noticed any effects from cold, heat or humidity.
I did a lot of sanding on my MPCNC parts and conduit to make them all fit snug but not over tight. I also didn’t tighten anything up very tight, like the parts holding the conducts or bearings. I sanded all my conduits quite a bit so they were smooth. I even chucked the conduit in a drill to spin it, first sanding then finishing it off with steel wool.