I made a cake for my brothers g/f this past weekend (my first fully covered fondant cake). I baked the cake on Wed. I put it in the freezer until thursday. I took it out thrusday evening and let it thaw. Iced it w/ buttercream (I havent mastered ganache yet and I like the buttercream taste). I used wilton fondant (YUCK, I know! but it was just for looks and I didnt have enough of my MMF or the time to make more). It looked okay when I finished covering it...it smoothed out and looked like it was holding its shape nicely (though I still have a ways to go on fondant cakes, it was harder than I thought it would be). I covered the cake and on Friday afternoon we took it to her. It was about 11/2 hr car ride. When we got there the fondant had bubbled out on one side of the cake. I ended up sticking a toothpick in the fondant and pushing the air out so the fondant would go smooth and flat against...eh' it looked okay, glad it was for family and they dont care what it realllllly looks like.
Sooo...what would have caused that? what did I do wrong? any tips on how to prevent this in the future??? TIA!!!!!!!!! I'm going to post pictures of the cake before the bubble appeared (later this evening).

Was it covered in an air tight container? If so, that was probably what went wrong. Fondant has to breathe or it will bubble or get gummy.

ahhhhh THAT MUST BE IT.....good gosh, I still have so much to learn!! Yes it was covered in air tight. THANK YOU!!!!

Yeah, no air tight containers, but I am sure that's not what caused it. How long after you filled and iced the cake did you put the fondant on? Cakes need to rest for a bit after filling to allow for settling. Sometimes putting a weight on top, like a ceramic floor tile (covered of course) or a cake pan will speed the process. If it hasn't settled, and the air hasn't escaped yet, and you put the fondant on, here comes trouble. Like air bubbles and blow outs.