mine are plastic housings.

 

The VisionX LED pods are plastic with aluminum ring around the outside. Very durable and still bright. They mount with very sticky double sided tape too.

 

Hey beecherr345 where did you get the blue cab light? They look great!! Are they bulbs or LED's?

 

LOL i have something just like that on my truck in iraq, there really good for spotting bombs lol

 

I'd do it this way (Assuming the dome light and cargo light have switched positives.) Drawing is shown with switch & therefore relay off.
That way if you've set the switch to "auto" either the dome light or the cargo light will activate them. Or you can turn them on independently, or off completely.