Carry on your truck a can of flat black spray paint and use it on the shiny metals that you want to take temps on. The readings will be close to using a TK or probe thermometer.
The RayTek I have, and it's done right well for me, is the Mini-Temp. It has an 8:1 spot ratio and cost me about $89US.
“Two things are infinite: the universe and human stupidity; and I’m not sure about the universe.” —Albert Einstein