Ok, a couple more questions:
1) Is it ok to combine two or more terrain brushes? If so, then how to I get rid of the wall that divides them. The wall isn't visible or solid during play, but it looks it could cause problems especially since there are two sets of vertices in the same place.
2) I got some invisible walls/slopes. What are these usually from, and how do you fix them. The walls/slopes are not visible in the game or the editor, but I can't move through them.
3) Why do my textures misalign after every rebuild?
4) Does anyone know where I could find (or would you like to make for me

) A small SAM site, a crashed spy plane, an airplane ejector seat with parachute out and lying on the ground, and a small keycard.