Doing my first four teir cake (6",8",10",12") and it will have to travel 2 hours via ground. Trying to figure out the best way to transport (in peices or together). And the best internal support system to keep the cake up and looking good. (Been Caking for a couple years but treat me like a novice for this one
Take it in pieces and just use whatever dowel system you usually do. Assemble on-site and you wont' be worried about it shifting and moving the whole time you're travelling., And make sure it's cold from the fridge and boxed up while traveling.
Remember to place some of the shelf sheet under it to keep it from sliding.
I'd travel with the 10+12 stacked and the 6+8 stacked and put them together onsite on their final resting place. Each set of 2 would be in a box with non skid mat under the cakes and also under the box in the car. Air conditioning on full blast all the way.
All cakes need to be on their own boards of the same size. I stack using wide bore straws [bubble tea, milk shake, etc.]. I'd have them in place in the 10" and just put some royal, buttercream, or softened fondant on top of each one before adding the top 2 tiers. No need for a central dowel this way, either.