The bride wants a buttercream wedding cake but she also wants fondant drapes. I'm concerned the drapes would be too heavy and pull the BC down. Any experience with this? Thanks.

I've never done it, but that's the first thing I thought of when I read the question. Maybe if you used a super crusting buttercream, and the drapes were attached more on the top than towards the sides it would work, if that makes sense. Could you do a little practice one?

Here's one I did this past week like that. It should be fine. Just roll the fondant thin and make sure you put enough on the top of the cake so it doesn't slide off and if your draping from tier to tier, you can wet the ends of the drape a bit so it sticks to the next one. HTH!

You could make a stronger cake like for doing a fondant covered. THen for added support use plastic dowls to support where the fondant is drapped down. Just a suggestion to help.

The cake in my photos with the draping is done on buttercream. As above, I rolled it thin and made sure enough was on top to not pull down anything. I stuck a toothpick in it to hold it in place and placed the flowers on top. It did fine on the ride in the car.