Ok, so I had to cut the front out of vanity for access to shower and it is pretty limited. There is no way in although if you had to get tore ain you could cut through floor if you measure carefully. They already cut throug the top part of floor to allow the trap to fit down in so you would only have to cut through the bottom board. This would be a little left of rear center of tire.
I am posting a pic of front of vanity and to the left and right underneath vanity
Ok, in this second picture you can see that a piece of 3/4" plywood on edge is what is supporting the drain end of shower pan. The drawer I spoke of is framed in also with 3/4" plywood.
Last picture looks forward under vanity.