Ok.. i have a question. we are having my sons b-day party.. june 4th.. at the park... and were here in good ol' California. Warm weather.
Will MMF hold up outside? what if the cake is in the shade?

Well, butter melts between 82.4 and 96.8 F. Shortening between 98 and 110F. Buttercream is made with either or both, so that will be an issue. Fondant holds up well, but it is sugar and sugar melts in the heat. Generally it is considered the most heat resistant. Only problem is, the buttercream that is underneath it so in your case you would want this buttercream to be made from the all shortening recipe. So, the best thing is to keep the cake in a shaded area. If you expect temperatures higher than those listed as safe for icing, you will need to keep your cake in a cooler until serving time. Maybe not the best thing for a cake covered with fondant, but possibly the only option.
Hugs Squirrelly Cakes