My camper also has a divided floor to ceiling cabinet in front of the pocket door area on the lower level and a bathroom cabinet on the other side. The top cabinet in my floor to ceiling cabinet has a removable panel, held in place by four screws. Like a normal pocket door mine has framing on both sides of the door to make the pocket for the door . My pocket space is wider than the door is thick
If you have the space, maybe you could use a thin cutter on something like a dremmel tool and cut your access panel. Then attach a frame (made out of some thin wood) on the backside of the cabinet (area where pocket door goes) of the uncut area leaving a small amount visible to attach your cut out section to. Glue or use construction adhesive with screws to mount the frame then use screws to attach your cut out panel.
Hope this makes sense.