The way to bend plywood is to steam it, but you need to make a form to hold it in place til it dries. Another way to bend it is to cut saw kerfs in the back side about half way through from top to bottom about 1/4" apart. I wouldn't trust it to keep its shape given the temperature changes a car goes through.
If I were you, I'd forget about 1/8" luan plywood and use 1/8" PVC foamboard. It will bend easily and stay in the shape you want after heating it with an industrial heat gun. That will be 10 times easier than trying to bend the plywood.
The picture is 1/8" PVC foamboard that I bent without even using any heat. It took me less than a minute to do that.
You could also use waterproof panel board. Anything would be better than trying to bend plywood.
No one lives forever, the trick is creating something that will.