James, I think that is one of the better sketchup models I've seen. You've worked methodically through it.
I hope you will continue to completion with as much enthusiasm.
May I suggest though that rather than do the interior, go back over the exterior and try and add some of the smaller details. Normally I wouldn't even bother with a sketchup model, but I think this one is worth it.
Stu
EDIT: From what I remember of Hoverspeed (HS GB???) It was open plan with a viewing area behind the bridge which looked out aft over the main roof. There was a bar area in the middle and the toilets and car deck access were at the back.
Have a look on google. I'm sure you will find drawings and photos.
Stu