Looks like previous owner added that plywood as a 'baffle' in hopes of directing airflow thru condenser fins better.
15*C (59*F) in food compartment and freezer 'frozen' could mean couple things.
Fridge on slideout ...........should have FAN(s) to help increase the draft from lower to upper vents
Fan has failed.......or no fan installed
12V DC computer fan center lined mid-position ----just above absorber tubes (large slanted tubing)
OR Cooling unit has obstruction/blockage allowing freezer section to cool but interfering with cooling process in food section.
Cooling unit replacement
What Dometic Model Fridge??????