Would be cool, if anyone knows how to
create and save a bitmap in 3SDG.

Probably with a plugin.

Such that i can save the top texture of the terrain, and then add it
in MED.
Currently I have it store in a textfile, and it needs to be painted
onto the terrain in the beginning of the game.

BTW, I use the default Multitexturing Terrain Shader from the templates.
It works good, and fast enough.

rtsmaker.com