I have never covered a cake mix cake with fondant. Is their any differences I should be aware of since they tend to be more moist than the ones of done from scratch?? Thanks

I almost always use cake mix cake, but I have covered one cake from scratch. I haven't noticed any differences. I have heard that you want a more dense cake for carving, but I don't carve at all.

I too have used a Cake mix cake under fondant and it was fine. If you want the cake mix more dense...you can add things like instant pudding or sour cream etc. to get that result
HTH

I've done it with no problems.