Thanks everyone for the advice so far. Exploration continued and more rot towards the rear so will post pictures when the floor is up. Currently in negation with all the screws and some are not cooperating. But we have ways and means.
I'll probably spend the next week honing my welding skills
![ROFL :rofl](./images/smilies/rofl.gif)
as I tend to miss the hole
![Embarassed :oops:](./images/smilies/icon_redface.gif)
on my plug welds and my straight runs tend to wander way off course completely missing the gap I am trying to weld together. To say nothing of my burn through. Hoping my new spotlight will cast a better light to see by.
I will also post a basic drawing to see that I understand how it all fits together - I now see why the panel I have is not correct (thanks Mike) but will cut and bend at the fake join.
I will also draw on the van where I am going to cut for advice ahead of major surgery.
The first embarrassing question and I rather hoped I would discover the answer before I had to ask ... is what are the closures?
The second question is how far up the panel should I cut. Clearly high enough to see what I am doing and gain access, but since all the metal is good I don't see the need to go much further than the rot.
Thanks