I have copies of most of my music CD's in my car on CDR's and have never ever ever had one fail. I throw them on my seats and dash, above my visor, or in a cd case under my seats.... through summer and winter..... never had a problem.
I know that CDs are susceptible to temperature changes (at least to an extent), but this seems more like a cheap media problem to me. I know I don't use some type of super CDrs, and Jersey weather gets mighty cold and awfully warm....I'd try using higher quality media.