I am doing a wedding cake in March that is long distance. I am baking the cakes the day before and traveling with them about 2 hours. I will be staying overnight and decorating/setting up the next day. Any suggestions? I'm making my icing and taking all that I need including extra ingredients for more icing and my mixer JUST IN CASE! TIA!

Depending on the size of each tier, put them into a cake box and put them on a non skid mat in the car. Make sure they are flat & level and nothing can fall on them.
I've taken cakes more than 5 hrs this way.
They were already decorated If not, at least iced and ready to decorate.
If it is hot you can fz the cakes overnight and they will be ready (thawed) when you arrive to decorate. Again, having them already iced is a time saver.

You do need your mixer because if you have made your icing ahead of time it needs to be whipped up again before you use it. As for transporting the cake, I make sure my box(I will cut one to size) or container fits the cake or board that it's on if the layers are assembled perfectly tight. That way the cake cannot move around at all in the container. that it's on

Is the design something that can't be done ahead of time? I did my nephew's cake, fully decorated, drove four hours, set it up and everything was fine. They traveled in cake boxes in the back of the vehicle. No coolers, no dry ice, no high-blasting air conditioning.

I drove a partial cake 5 hours-finished on site in the reception area. Took some old sheets and put on the floor to catch any stray icing. The tiers were finished and all I did was stack and put the borders on. I put each tier in a box on a non skid pad and the box on a non skid pad.
No problem.

I'd just decorate it, stack it, chill it really good, and take the whole thing fully assembled. Make sure it's really sturdy for support, box it up, and go.

If you're staying overnight, check and see if there's somewhere cool (or a fridge) to keep the cake overnight (depending on icing/filling), but I always fridge mine, every time.