thanks for the replys
At the moment i cant take the belly pan off as we have 4" of snow in North Devon England.
So i decided i would go inside and make a start on trying to take the floor up. fisrt job was to take the side panel off that was a easy job. once they were removed i could see the U channel where the outer skin rivets onto it. when the panel was removed i found the water leak 1 was from the waste pipe air vent in the roof leaking down the panel onto the floor (same on both sides) and the other leak was from the rear lights where the wire comes out there was a stain down to the floor.
I could also see the bolts holding the U channel onto the plywood floor. They were rusted in so had to gring them off. when that was done i the cut the ply floor into small sections to make it easyer to remove.
On the offside the floor had 15mm of fiberglass on the top!! did not see that until i started to remove the floor.
Once the floor was removed i could see what the frame was like and to my suprise it only had surface rust on it.
A quick rub down and some paint and i can make a start on putting the new floor in.
few pics of the frame and the water stain,