You will need to remove the door and frame complete. This is screwed in from the outside of the caravan, screws being underneath the plastic herzim strip. when all screws are removed ease the frame from the caravan and clean off all old mastic. Remove existing wood from the wall where replacement is required.
The new wood must be cut to the exact size depending upon the thickness of the wall. Glue into place using a polyurethene adhesive.
Replace the door and frame using a non setting mastic sealant such as Carafax IDL or equivalent. Secure with new screws.