Normally the underlayment goes up to the tub, somewhat submerging the apron a bit. A good vinyl installer can make a tight cut to the tub, leaving just a smallish gap for the Silicone caulking.
I have a Villager cast iron tub going in. My old cast tub had tile up to it, so the "lip" was covered. This tub technically doesn't have a lip but the enamel isn't even either. Anyway, I have a vinyl floor going in with the new tub and am very concerned about having a cheap line of caulk where the tub meets the floor. Is there an elegant solution to this?
Thats what I was thinking and I have never done this before. Unfortunately I got the tub installed on top of the underlayment