ASo my brother's getting married and I'm in charge of the cake. I've never transported a cake such a long way and I'm a bit nervous. He lives about 9 hours away. I have the fortune of using a commercial kitchen when I get there to ice, assemble, and decorate the 4 tier cake. So I have frozen the individual cakes to take on the drive with me tomorrow.

This is stupid but can I just put them in a big Tupperware box and will they be okay? I worry about stacking them on top of one another without support. There are 8 cakes, each of which is 2" high (12", 10", 8", and 6" square cakes).

It's the little details, like how I'm going to drive them across the eastern seaboard, that I may have perhaps missed. Ugh!

I would not stack all those up.  Way too much weight.  Use smaller containers and I would only do 2 layers on top of each other, maybe 3 if you had to.
 

Keep the cake layers in their individual wrappings.  Pack them into a picnic cooler with as much dry ice as you can stuff into the corners.  The idea is to keep the cake layers FROZEN solid for as much of the drive as possible.

When you get to the site, let them that as you would do normally.

We drove 1400 miles over 24 hours with 2 frozen cakes - one bc and one fondant - and they made the trip just fine.  Since your cakes are already frozen, just keep them in a cooler with dry ice.  When you get there, let them come to room temperature before unwrapping so any condensation will be on the wrapping, not the cake. They'll taste as fresh as if you made them there.