I guess it all depends on if coming from sketchup, ac3d recognizes the original mapping or not.
In AC3D for my simple model I had to select things in face mode and then map them in TCE whether it was top or bottom left right etc. Then I resized it all to fit in the box, exported the UV map and used it as a template to paint the textures and then loaded that.
Hopefully someone will chime in with more help.