So Im traveling about 45 minutes to deliver a wedding cake tomorrow. It is a 3 tier cake. Im going to assemble when I get there. My tiers are 12", 9" and 6". I did a crusting buttercream and Im wondering what the best way to transport this is? Im worried about bumps that could cause the buttercream to crack... any ideas...

First, make sure it is supported well (no matter what system you use). Use non-skid material under the cake board. Keep the air conditioning on. You'll be fine