We stripped the outside paint, removed all windows and resealed them using Sikaflex marine, restored the four seasons hatch, replaced the full running gear ( axle, brakes and tyres) resealed the J rails and roof seams and painted with premier plus 4 coats of paint.
Inside we removed the old vinyl floor and replaced it after giving a good coat of decking oil to the plywood floor.
The cabinet doors were replaced with marine plywood. All the interior was painted. Beds restored and new matters bought.
The end result
A video of the caravan finished is here: https://www.youtube.com/watch?v=8RHJzg0yicI&t=76s