To be honest with you their is only so much you can get right with the detailing of these subjects, When I built Cardiiff I had loads of photos and the experience of serving on her for 3 years. No matter how exact you get your project there are always going to be changes made, I remember that you could go away for the weekend and come back on monday morning to find the dockeys had stuck something else on.
I was quite lucky with Cardiff in respect that she was decommisioned shortly after I built her, so for one, It shows her as it was before the decommisioning and two, no-ones going to know because shes not around anymore.
The way I would tackle this subject is to as Holmsey said "get loads of pictures" ,try Writing to the "Ships liason officer" on board and explain what you are doing, you never know you might even get an invite to look around your subject, or at least get some photos from them.
Hope all goes well
Phil