Bgreenwood - I moved your post to the "General" topic, hoping that maybe others would chime in as well.
Yes, I have done both - covering walls in fondant (which I found very time consuming and only did once), and flooding walls with thinned Royal Icing. Hands down, I would choose flooding walls over mixing/buying fondant, rolling fondant, applying RI as smooth as possible, then covering with fondant. Way too tedious for me.
Plus, flooding will naturally level off and provide a smooth wall in order to airbrush. In my opinion.
A trick that I do to create sturdy walls, no matter how I am finishing the outside walls (leaving natural/gingerbread, flooding, candy/cracker covered, etc), I always, always,
always frost the inside of large walls and roof sections (before building structure) with a thick layer of Royal Icing to provide me extra strength. (see attached pictures)
Hope this helps! I look forward to seeing pictures when completed.
