There was an "OSB"
sub-floor under the carpeting. It is still there as a base sub-floor but we have decided to cover it with oak plywood before we put the vinyl down.
We had to remove a strip of carpeting that was left under the slide-out edge before we can lay the oak down. This was not an easy process.
Here is a photo showing the carpet strip-
-and here is a photo with it removed-
I am sure I will have another photo up soon with that area completely covered with oak plywood!
(PS-when I mention "we" above as having to do things- that is actually me more than likely 'supervising' and my DH doing all the work!