This a great reason for making car copies of your CDs and keeping the originals in the house. I bought a really nice felt lined CD Case and make copies of all of my "road discs" The only original ones that I carry are new discs so I can see if I want to make a direct copy or pick and choose songs. TDK makes a scratch resistant disc that works great for harsh environments.
I also transfer the disc to my MP3 file with MusicMatch Jukebox, but actually make a bit-for-bit copy of the disc for the car.
The heat may be worse if you load up the changer with 6 discs. Basically 6 heat sinks inside the unit. I agree with UPS_er this does not seem right. The discs should never get too hot to hold. Unless you park in the AZ sun for 6-8 hours and eject the disc as soon as you get back in the car. If this is the case, you should probably get a Sunshade for the front window or a dashmat.
Steve