My cousin's wedding is this weekend. Its an hour away. She has requested a 4 tier, white on white buttercream main cake on to which I will place fresh flowers. I'm debating...do I transport it stacked and fully decorated or frost each tier, and then stack and decorate once I get there. I will be using SPS but buttercream is a pain and the roads here in the midwest are awful.

I, personally, am scared to death to transport a stacked cake. Sometime I'll do a 4-tier in two separate pieces. I always arrive at the venue with PLENTY of time to stack on-site. I also take my "tool bag" with me to help with any incidentals. Hope that helps!

As experienced as I am I still would NOT transport this cake fully put togethers.
Depending on the sizes of the tiers I would put the largest 2 together as one unit, then upper 2 together, then stack the 2 part together when at the venue.

Why do you feel the b'cream is a pain? I work(ed) mostly w/b'cream so for me it would be a breeze.

I have tried it both ways, several times. And honestly, the stacked transport always went much better! (For me, anyway). It just seems that I an into to many issues after arrival with a non stacked cake, even with giving myself plenty of time. For example: arriving at the venue - and they don't have the cake table set up. Or... not being able to properly detail the cake... I could go on and on with the bad experiences I have had.
If stacked correctly, and driving carefully (I recommend taking someone with you to ride with the cake), the stacked cake will be fine. Make sure you have a good support system! Always take your tools just in case.

Hope that helps!

I have confidence in the SPS but if you breathe on buttercream wrong it gets a mark. With fondant, it firms up. When I stack fondant there are not many marks to repair. I cannot seem to master the art of stacking the buttercream without having to do some major repair work.

The tiers are 12/10/8/6. I could do as others have suggested and stack the bottom 2 and top 2. when I get there I could add a border if needed and finish up. It may reduce my stress level and chance of heart attack

I always stack what I can lift.

I can lift a 12" round, 10" round, 8" round and 6" round cake. So for this cake I would deliver stacked.

the 8/6 top 2 may be a bit top heavy and could fall in transport. Find a sturdy box tall enough but not oversized for them - that will help cut the chance of it falling over.
To put the cake in and (more importantly) out seal up the top and cut down one of the sides so you can slip it out rather than life it up & out. Tape that cut side well until you need to take it out.