Go to rally's and Airstream meetings, look inside every Airstream you can get to... take photos of what you really like, make notes on the year, materials used, etc. You can also look at all the photos here on the forum (might take a while!) and get ideas as well. It all depends on what you like/want. Bathrooms are usually very individual according to ones likes. I have seen many folks use their bathtub as storage only... so I have wondered why not keep a smaller shower and make more storage... Are you 6' 4" or 5' 3" all of that makes a difference!
If you are going to all the trouble to completely re-do and not just renovate or restore, you might as well make it what you like and want.