I rolled the rear bulkhead to transition to the floor.
Then I ran the floor panel through the Pulmax to form the ribs as before. It picked up a twist which I think was caused by the stretching of the interior, so it required a couple passes through the Shrinker. That corrected some of the twist, but I had to use the torch on areas the jaws wouldn't reach.
And then it laid flat when Clecoed into position.