Oh yeah! It was over 100 degrees...Just checked under the trunk carpet and it is bone dry No signs of anything unusual. I'm really leaning toward an overflow situation.
BTW, bad lighting led me to think that the tank was empty; in fact, it is only slightly below minimum level, further leading me to a hot day overflow scenario. I will add a bit of distilled water and call it good, I think, seeing as it never overheated.
Thanks all!