jane, are these going to sit outside? If so, you might want to consider the
cooked icing that uses Crisco. It doesn't TASTE like Crisco--it's actually very light. But there will be no problems with it sitting outside.
You can make the same icing with full butter or partial butter as well, but I don't know about how long that can sit outside.
Shirley Corriher uses a white chocolate/cream cheese icing for outside weddings. I've made Rosie Beranbaum's version of this (which adds butter) and it is delightful. The good-quality chocolate provides all the sweetness you need for the creamcheese. I used Lindt white chocolate.