I see this is your first post, but you may have been reading the forum for a while. One tool that I didn't immediately pick up on was the "SEARCH" tool. If you try clicking SEARCH and entering "bathroom restoration" or "Globetrotter Bath" you may be amazed at how many threads you uncover. I'm sure you'll meet many fellow restorers who can help you out whether you want to do a "historical preservation/restoration" or want to customize blending newer materials and technology into a classic shell.
I have great respect for the people who do the Airstream Rescue - but I owned an old house and decided I needed a vacation from constant projects, so I bought a new one. It's all good.
Play with SEARCH - sometimes it takes three or four times to find what you want, but it's a goldmine when you do.
Oh, and if you have to build something from scratch, very few people realize you can get Corian (or other similar brands) in 1/4 inch thickness - useful for shower WALLS. It can be shaped easily in an oven at fairly reasonable heat - but it's generally not a do it yourself project - unless you own a restaurant and have a pizza oven! The base would need at least 1/2 inch with some reinforcing. The main worries would weight and cost. The main benefit is it will last forever and can be scrubbed! There are also NO seams to grow black mold or leak onto the floor.
Good luck on your project.