Creating auto-trace mask from roto brush information to be applied to a new layer

Hi there, hoping someone may have an answer to this problem.   I've roto'd a layer  (layer 1) and I'm looking to take that roto info  and make a keyframed mask out of it in order to apply it to layer 2 so that I can have layer 2 masked with layer 3 showing through and scrap layer 1 altogether ( I just needed the shape/ motion fro layer 1).   I found tutorials that suggested auto-trace in order to achieve this but when I apply auto trace (even after freezing the roto) it only allows me to create a static mask from a single frame or selects the entire frame so that I have a 16x9 rectangular mask and completely ignores the roto information.  Has anyone had experience with this issue or does anyone know another method for creating a keyframed mask from a roto that can be applied to a separate layer?

Thanks in advance!  Ps I am using the most recent version of AE