2017 thermostat

[Kansas100]

I’m gonna change my thermostat on a 2017 2500 6.4. (90K) My question is do I need to replace the housing as well or just the thermostat. Or is the wise thing to replace both at once just to be careful.
Thanks in advance.

 

[flan]

Are they plastic like some vehicles?

 

[Kansas100]

So the housing I purchased came with the thermostat.
It would appear the thermostat is 2-stage and the first stage was stuck open.
Previously the truck was running at 185 degrees and now it floats from 200 to 210.
Obviously the heater works better and mpg has improved.