Do you see the texture file in your palm folder in outerra?
If not then you need to find the original texture file, convert to dds and move manually into your palm folder in outerra.
You will then have to make an opacity mask (black) leaving the silhouette of the trunk and leave white, save as dds then add the name next to the opacity line in .mtl file
Then Set color to 1.0,1.0,1.0,.999 (.999 is for tranparency, it need to be below 1.0 to get a very slight transparency for the opacity map to show in game.
As for the size of the model, in sketchup in the fbx export menu, clic options. There i usually select 'cm' as the unit, but you can try others and see.