I'm going to be transporting a  wedding cake in May. It's not more than a 30 minute drive but with every other wedding cake I've done, the buttercream slides off the sides of the cake because it gets too hot. I've tried cranking the AC up and placing frozen towels over the cake containers while traveling and neither of these seem to work. I've heard that you can use dry ice so I was going to give this a try. My plan is to keep the tiers in separate air tight containers, place them int he bed of my husbands truck and just place the dry ice back there with the cakes (securing the cakes so they don't slide of course). Does anyone know if this will work???

I think a better solution would be a heat stable buttercream.

Leah, do you have a heat Stable Buttercream receipe?  I about cry when I cant keep the buttercream on the cakes and all mine are buttercream.

Try Sharon Sugarshack's buttercream. It doesn't matter how hot or humid it is my icing stays right where it should. It never sweats or slides off.

I agree with Leah...the problem is your buttercream. 

Here are two SUPERB high-heat, high-humidity recipes. I have used both and prefer the Indydebi recipe. However, I live in So. California and is is NEVER humid here. Ricki's recipe may hold up better in hot/humid conditions. Important: Even though both recipes say "Crisco", these recipes were used for 30+ years BEFORE Crisco changed their recipe to NON-TRANS-FAT. The current Crisco does NOT perform the same way it did 2 years ago.

Where the recipes call for Crisco, substitute (if possible) the following:

BEST BY A MILE: High Ratio Shortening (this is only available from specialty cake stores or online. You cannot find this at a grocery store.)

2nd BEST: Grocery store brand white vegetable shortening that still lists 2-3 grams of trans-fat on the ingredients label

Use only as a last resort: White Crisco (not butter flavored). It will still work, and nobody else but you will know that it is a little grainy and not as smooth as it would be with one of the products in 1st or 2nd place above.)

INDYDEBI CRISCO-BASED BUTTERCREAM--(Excellent for hot/humid areas):

(IndyDebi is a very experienced decorator/caterer: http://cateritsimple.blogspot.com/)
Single Batch Recipe:

1-1/3 cups Crisco (BETTER: store brand shortening with 3 grams of trans-fats, or BEST, a specialty cake supply product called high-ratio shortening. As of 2010 Crisco no longer contains trans-fats.)

1/3 to 1/2 cup milk, depending on consistency needed
3 Tbsp powdered Dream Whip (powdered whipped topping mix made by Kraft Foods)
2-3 Tbsp clear vanilla, depending on personal taste (optional: almond extract, or lemon extract )
2 lbs. powdered pure cane sugar
IndyDebi says: “There's no wrong way to mix this. I usually mix all but the powdered sugar & milk for a minute or two, then gradually alternate the sugar & milk, but the only reason I do this is to avoid the "sugar-splash" factor. The longer the mixer runs, the smoother it gets. Sifting the powdered sugar before blending helps with smoothness but is not necessary.”

NOTE: Based on recommendations from other users of her recipe: 1) I make a double batch so the beaters are totally immersed to avoid air bubbles, 2) I beat the shortening, milk, Dream Whip, and vanilla for 10-15 minutes BEFORE I add the powdered sugar. I refrigerate or freeze leftover icing.

My cousin RICKI'S CRUSTING BUTTERCREAM that she's used for 30 years in hot, humid Kansas:
Ricki's Crusting Buttercream (high-heat, high-humidity)
1 cup + 4 TBSP water
2 cup Crisco (use high-ratio shortening if you have it)
½ tsp popcorn salt
1 tsp butter flavor
1 tsp almond extract
2 tsp clear vanilla
8 tsp meringue powder
4 TBSP cake flour
1 cup corn starch
4 lb. C&H sifted powdered sugar
The recipe above is a double batch. Any leftover icing will be ok in the fridge/freezer.

Well, yes to all of the above!

 If your BC doesn't last longer than 30mins out of the fridge there seems to be something wrong.

 I live in the tropics and never had BC melting off the sides of a cake (except for my first trial making smbc.

 What I have learned is that recipes are a guideline and don't have to be followed to the dot, especially if you use them in another environment. For example: Butter, obviously my enemy in this extremely hot climate, will simply melt if I leave it out on the counter - literally. So, making smbc, I want to use as little butter as possible if it wants to survive on display for some hours. ABC needs way more icing sugar and or shortening. Still, I prefer to refrigerate the cake before delivery/ collection (also because of VERY bad road conditions...shake shake shaking the cake in the car, lol) and to give it an extra kick start so to speak.

 I know some people don't like placing cakes in the fridge, but that's another topic and -again- depending on your location (and roads

That's so wired...half of my post disappeared...!

 Anyway, long story short...unless you want to bride and groom to cut the cake in a walk in freezer (sorry, guess you can't laugh about that...yet!), try one of the above recipes, or others, and make adjustments if necessary.

 You gonna feel much more relaxed having a reliable BC recipe and don't have to worry about dry ice and frozen towels!

That's so wired...half of my post disappeared...!

 Anyway, long story short...unless you want to bride and groom to cut the cake in a walk in freezer (sorry, guess you can't laugh about that...yet!), try one of the above recipes, or others, and make adjustments if necessary.

 You gonna feel much more relaxed having a reliable BC recipe and don't have to worry about dry ice and frozen towels!

Google Charlotte's Whipped Cream Buttercream.  I've used it for years.  It's an ABC but based on meringue, so I refer to it as AMBC.

Do you use alot of butter in your buttercream recipe?  You might want to use more shortening and less butter or none at all and instead use a butter flavoring.  I've used buttercream for years and it has never slid off my cakes.  I keep them in the frig until delivery and then each tier is in a box for delivery with the A/C cranked up in the car.