I'm using Mojo heightfield outputs. Getting stuff out of TG2 seems a lot of hassle. You can get .ter files but then you have to convert those. Supposedly you can get .exr out. I can't get that to work but at the end of the day it's best to get terrain from elsewhere. TG2 is not as good for terrain as some other apps.
You bring in a flat plain of polys then apply a displacement texture to it - your heightfield. This then displaces the flat polys obviously. Then you just get to work with all the immense power in 3D Coat to paint whatever you want. You then export that displacement texture. You can create your own brushes, you have layers, you can even bring in another picture move it around and stamp in in. There is no point in even explaining anything. You can do everything with this app. Tablets are awesome though because then you have vast variation with the brushes.
I'm still experimenting but I may post some screenshots of some terrain being worked out.