Help! I live in Texas where it is currently 95-100 degrees hot all summer. My house is probably around 77 degrees.

I just made a cake with SMBC icing, put it in the fridge overnight to firm up and then covered with fondant. The following day, the fondant had started to sag. I think that the SMBC gets so soft in this heat that the entire cake compresses from the weight of the fondant.

I love SMBC -- any suggestions for another frosting or a trick to make SMBC more firm?

Thanks in advance!

I can only suggest the Wilton buttercream which you will find on their site. I use it for teaching cake decorating because it is all crisco with no butter and stands up to hot hands holding icing bags for a long time. I personally don't like to use crisco but have had to in some cases. Most people don't know the difference because they are used to eating icings on baked goods from grocery stores which is pretty much the same as the crisco recipe, unless it's a high end bakery you don't often see real butter or cream products.
I know I hate to do it so if someone else has a better answer I'm all ears.

This one tastes good and can be used in the heat. HTH
http://www.cakecentral.com/cake_recipe-6992-0-Indydebis-Crisco-Based-Buttercream-Icing.html

Yes, I would go with Indydebi's BC like mjk350 suggested.