This looks like a Sketchup problem, caused by one-sided textures. SH3D gets confused and can't choose whether to show the textured or non-textured side.

If that is the case, the solution is not very difficult.

Install Sketchup, download the model in SKP format.
Open it in Sketchup, then export it.
In the export dialogue, click OPTIONS and make sure to choose "double-sided textures" or something similar. (I haven't Sketchup installed, so I can't check the exact wording.)

Hans