I don't know how you do it in AZ or TX, because I struggled all night to get a recipe of French BC to come together. It was 106 yesterday afternoon, but I had the air on. 

anyway, it came MOSTLY together after rubbing ice on the bowl while it mixed. Finally, I dumped most of it out (I was making a triple batch) and added cold butter to it. It took a 1/2 of butter to get it to the right consistency. I was so frustrated!

Gotta finish it tonight. 150 cupcakes for tomorrow. Luckily I have plenty of cold butter in the fridge.

Any tips?

if you ice cold cupcakes (if your regimen allows) you can help set the icing that way as soon as it's applied and counteract any more melting before its time

I always use 1 C butter, 1 C Crisco blended well then add powdered sugar and whatever flavor is called for and something to thin it a bit. Has never melted and doesn't crust. As long as butter/Crisco measurements are the same you can make any size batch. Still has great flavor and texture. Give it a try.

well come to think of it--you have to keep french buttercream --the egg yolk kind-- refrigerated so yeah chilling the cupcakes before icing would help you out there