Not to beat on a dead horse regarding the metal lens holder, but a friend of mine worked for a business that made FRP products. They had a 2-level warehouse, and it was not air conditioned. The second floor was where they cut the woven fiberglass sheets. They had a wooden cutting table, with a sheet of 1/4" plastic affixed to the top.
In the summer, the 2nd floor would get hot, due to the lack of air conditioning. The plastic would expand more than the wooden table, and would become "wavy"-- it was screwed to the table in a few places, and in-between those places, it would bow up off the table several inches, making it quite difficult to make accurate cuts in the fiberglass sheets.
Everything expands a little when it gets warmer, but at different rates. Metals don't expand very much, but plastics expand considerably.
A camera lens assembly has several (glass or plastic) lenses contained within it. The distance between each lens is critical to achieve a focused image. If the plastic housing from the sensor to the lenses expands by a few percent, the focus will become unacceptable, and you end up with a situation where the camera's focus might be good when the car is cool, but atrocious after it's been parked outside in the sun for an hour. And it might also go out of focus in the winter (in colder climates), as the lenses get too close to the sensor.
My strongest recommendation is for a metal lens housing. I don't know if the base has to be metal or not, but certainly, the tube from the lenses to the sensor should be metal.
but what we can do is test the available lenses and do a cost/benefit (is it worth it) analysis.
