Absorption fridges require very tight clearances to control draft (airflow) up thru absorber tubes (large slanted tubes) and then across condenser fins (at top) before exiting.
RV Mfgs have a bad habit of NOT following Fridge Mfgs Installation Instructions
Side walls, top and bottom of fridge should have ZERO Inches (0") of clearnace and back space should be no larger then 1" of clearance
IF fridge is installed with large clearance on backside then 'Baffles' should be used to direct draft.
Dead air spaces will cause airflow to stagnate ---build up hot spot.
And when fridge is installed in a slideout 'fans', baffles are most certainly needed.
Sounds like that 'plywood' is an attempt to clse off dead air space at top of fridge AND act as a baffle to direct airflow across condenser fins then exit via top side wall vent cover
Not sure which model you have....appears that it is a Dometic due to condensation drip hose sticking thru lower vent cover---Dometic does that. Norcold doesn't.
Anyway here is an example of Installation Instructions for Dometic Models---may have yours.
http://www.dyersonline.com/downloadf...tfile_id/2823/
And this is a generic fridge ventilation in a slideout with deflector/baffles