If using melted chocolate, is there something I can add to make the product last longer?

I’ve seen a few articles on this. Here is one. Perhaps tempering will help the chocolate keep it’s flavor too. Hope this helps. =)

Tempered Chocolate

While those little white spots are not attractive, the good news is that the candy is still safe to eat. In the future, when making chocolate candies, refrigerate them for about 10 minutes to set the chocolate—this will help keep the high gloss and firm texture you want. Then store the sweets in a cool dry place. Chocolate that comes in contact with moisture or becomes too cold during storage can develop the tiny white or gray sugar crystals you noticed. And, when candy is stored at temperatures in the upper 70s and higher, white streaks or dots may develop on the surface of the chocolate. To prevent this, chocolate that contains cocoa butter must be tempered. Tempering is the process of carefully melting and re-cooling chocolate, which allows the chocolate to stay glossy and firm. Without tempering, the chocolate can develop a grainy dull blotchy-gray surface.

Only chocolate that contains cocoa butter requires tempering. Chocolate confectionery coating, an ingredient in many Taste of Home candy recipes, does not need to be tempered because the cocoa butter has been replaced by other vegetable fats. Confectionery coating melts easily and maintains a smooth surface, making it a good choice for many candy recipes. When purchasing chocolate to coat candies, be sure to check the label and the ingredient list for the type of chocolate and the fat content. If you do use chocolate that contains cocoa butter, it’s best to refer to a candy cookbook for details on how to temper it.