Any chocolate and/or white chocolate buttercream recipes that are really good, that don't use real butter? I need something that can hold up to heat and travel well.

I like to use Sugarshack's buttercream made with shortening, I use white chocolate mocha creamer for the white chocolate bc and I vary which chocolate flavor creamer for chocolate. In the chocolate bc, I replace 1/2 cup sifted cocoa for 1/2 cup PS, and when I am mixing the creamer with the shortening, I add 2 oz unsweetended melted chocoate, and one melted semisweet chocolate bar. If you want a really dark chocolate color, add some brown coloring.
We've had a lot of triple digit temps here, and this held up well.