I'm making a 2-6" cakes on 2-8" cakes. I'm using fondant my question is do I put this together before I get there and if so how do I get the top layer from not moving. Do I just put icing on the board and sit it on the fondant will it not move.. This is my 1st stacked cake I have done, any help with be great.

Make sure to dowel the 8 inch cake to support the 6 inch on top. I usually put a dowel down through the top of the 6" through the board and into the base, that way the cake won't move anywhere.

Here is a tutorial by Edna on youtube

Exactly what mrswendel said.

To stack or not to stack, I really don't like transporting stacked cakes. I have, but never feel really safe. I would def recommend dowls and make sure your cake structure is sound. I found that mix cakes somtimes are too moist, the rods can tear through the side of the cake, especially if there are not enough. Distribute the weight load, it decreases the pressure on your indiviual stress points. As for getting the top to not slide around on the fondant you can use a bit of frosting, piping gel or even royal icing. royal icing does not have as much moisture as bc so it shouldn't leach wet spots or grease spots onto the fondant. I did just a couple of weeks ago transport a small 10 and 8 in two tier about 30 miles, make sure it is sitting level in the vehicle, like not on a seat and have the ac on. Try, if your windows are not tinted to have the cake out of the direct sunlight, it warms the cake and can cause a lot of damage in a short time. I have one last tip, my DH is a carpenter so I have him sharpen one end of my dowls for me, they sink into the cardboard of the cake board and stick tight. You can sharpen them yourself with a grind wheel, sharp knife or craft knife. I have also used chopsticks and then cut them to size cutting off the blunt end so the pointed end can sink into the cake board. Good luck!