IMO, it is VERY doable. If I were doing this project, I'd give the tub a thorough cleaning/sanding, then I'd use thinset w/a polymer admixture for the adhesive. In some climates porcelain is suggested for your purposes. Check w/your local tile store. If I were in your place, I'd use the thinset also for grout. Be sure and post pictures of your WIPs.

YES! Very doable! I go to a tile store(specialty, not Home depot) and get some outdoor> mortar, sealer, grout, maybe ask them if they think if diamond lath would help build up the base? And I would use porceline, slate, rock, glass, as I have been here on Vancouver Island BC, and have found thru trial and error, that these are the precautions I use now for long term success with our weather.

Thanks so much for your thoughts Calamity and Slowmedown...I'm going to hunt down the materials and start it this spring. I'll post photos when I get going.

Again, I really appreciate your advice!