So if I'm working on walls, doors, etc and I hit mud or something that gives me a "terrain won't support" error...is there anything I can do to beef up that area to build on it?
If i'm not mistaken you can use the moisture pump to get rid of the mud. I haven't used it yet personally but Tynan mentioned that it can take a while though depending on how big of an area you want to clear up.
yep to build on mud and marsh you have to use the pump, its slooooow though.