I apologize if this question gets asked over and over, but I couldn't find a good solution.

I'm selling cupcakes at a farmers market that's located outdoors on a paved parking lot, and after a couple hours my buttercream frosting starts melting. Is there anything more I can do to stop it?

Here's the details: I package my cupcakes in plastic snap-close clamshell containers and store them in a large plastic storage bin, under the display table, which is under a tent-roof-thing. I use all-butter-buttercream since that is what my customers like and what I think tastes best, and I use a high enough ratio of powdered sugar to butter and flavoring that it is very stiff when I pipe it on the cupcakes. I only display one of each flavor at the market and hide the rest from the sun, but for some reason that is causing great confusion amongst the customers who then think I only have four individual cupcakes to sell because they can't see the rest (lol).

Despite all this I'm still having some melting issues, and it's wasn't even that hot this weekend (upper 70s - low 80s).

Should I add ice packs? On top or bottom of cupcakes, or both? Should I add meringue powder to my recipe? I don't want to switch out some of the butter for shortening in the recipe because I've never been able to get as good of a taste that way (maybe it's just me).

Add ice packs to the top of your cupcakes (cold air sinks).  Think about bringing extra ice packs in a cooler as well in case the others thaw out.

And I always mention that if a cupcake flavor "looks low", etc. I have plenty more.  This is what I do for my cream cheese cupcakes.  Once I tell them I have more, they say, "Oh, okay, great!" and it's not an issue.

Make sure there is no way for the sun to hit the containers.  At my market this Saturday it was I think 80 and the sun started melting the cupcakes in the case.  Everything out of the sun was okay.  Consider covering the bin with a white sheet/towel to help with this.  And since you're on a paved parking lot, consider setting your bin of cupcakes on a bread crate to let air flow underneath.  The hot pavement may be heating up the bin.

I hope some of these suggestions help!