When we renovated our coach, I faced the same problem when trying to remove one cabinet.
Learned that after the cabinet was installed, false interior walls and floor had been built to hide all the carpentry installation work, making the interior of the cabinets totally smooth. The walls were precision cut and pressed into place. It took a bit of careful prying to get the wall pulled away. Then it was simple to remove the screws holding the cabinet to the wall.
Jim & Kate
2016 Creekside 23RKS, 2014 Ram 1500 Eco Diesel
1995 Monaco Dynasty 36', 2005 Honda Pilot