Well Fox, here's what I use for my Forests:
square part 1 data3d\les ctverec pruchozi_t1.p3d
square part 2 data3d\les ctverec pruchozi_t2.p3d
Forest - triangle data3d\les trojuhelnik pruchozi.p3d
And for the type you can find on Malden use these:
data3d\les_su_ctver_pruhozi_t1.p3d
data3d\les_su_ctver_pruhozi_t2.p3d
data3d\les_su_trojuhelnik.p3d
About objects appearing flat in the WrpEdit preview window, I have seen this too.. and usually fixes itself when you get it in game.... I know this is true for bushes at least