Finally dug this up after a long time of searching. It's an excellent tutorial on creating outdoor levels in WED, by Willi Leopold. It's probably the best WED-specific tutorial out there, and definetly worth the read for any aspiring level designers. Hopefully someone will find it handy, it's a shame so many good resources like this seem to vanish...

http://www.mypage.bluewin.ch/lhp/games/leveltut01eng.html