We just replaced 3 rb153's with 532's
Just after that we got a BIG cold snap. Our 3 new 532's are in northern wisconsin and have been running consistently for the past 3 months with no problems or outages whatsoever.
During this time the temp has gotten down to -40 w/wind chill. The temperature there can sometimes swing 40F between day and night.
We use outdoor sealed plastic boxes and set the cpu-mode to regular during the winter. Seems to be all we need to do..
system routerboard settings cpu-mode regular
although... we are R&Ding a larger outdoor solar powered box with a integrated heat exchanger (don't ask, so far we can't find a way to make it cost-effective and may just need to build them one off for us only)