One solution:download Magic World. You can create multiple matrices, matrices bigger than db normally allows, accurate place 3d objects on them (such as trees), automatically set objects to ground level, and all other sorts of stuff. It can also load MatEdit1.5 and possibly 1/6 matrices.
The best part is it saves your world as an .mwdb file, and the software comes with a function to load the world into your game, and it comes with a working demo to show off what it can do.
Magic World is a beautiful thing.
Juvenile Industries
Current Project: The First Room (FPS)
Soon to come:An rts, and a snowball fight game