Storing chocolate at home in the summer
There are three different crystal types in solidified chocolate with one of them being the prefered type.  This is why we temper chocolate, because it promotes crystallization of the prefered type. 

From what I recall, the ideal temperature for chocolate is 70&deg;F and the first type of crystal in chocolate starts melting at around 82&deg;F.  So while not ideal, you should be fine with the room at 78&deg;F.  Keep in mind Lindt chocolate with milk is a little softer than their darker chocolate line. 

You can simply place the chocolate in a cooler (like a coleman) along with a pop can that has been in the fridge. The cool can should prevent the chocolate from getting too hot. Switch the can with another cold one daily and that should keep the snap sound in the chocolate along with the taste.