We had a fiberglass tub in our Rage'N Toyhauler. With all due respect, your wife would have to be mighty "short-legged" to use it! I think is was designed with kid's baths in mind. I think it was only 48-54" long.
I have been searching and for the life of me I can't find it but at the little York, PA RV show this past March, there was a toyhauler (SOB) that had a decent sized tub in it. It took up some serious real estate and had a gray tank dedicated for its use only.
If I find the name, I'll post it here.
On edit: 2009 Inferno 4005 SL has a different version of a tub.