It's not difficult, just very time consuming. At least the way I do it - making each individual frame as a .png and then combining them as layers in GIMP.
Here's my first iteration of the wrecker floor plans:
It's a difficult ship to work with, though. I love how it looks, but the in-game model suggests that it is far, far larger than the model's appearance. Having the entire front section an open "window" makes it look like it should be the size of a heavy freighter or small gunboat, but the physical size of the ship (flying it next to other capships) suggests that it's the size of a large gunboat or small destroyer.
So coming up with realistic floorplans proves challenging. I chose to make it a bit on the smaller side internally, but to leave a lot of open space in the front to fit with the huge windows.