You'd be prudent to indeed inspect the rear region of your absorption refrigerator.
There could very well be a fan back there to aid in upward draft. They are optional in older models, required on many.
There is probably a small flue chimney like tube with a screw like baffle in it, above the burner assembly. Mud-dobbers, (wasps) and spiders love nesting in gas appliances. Anything is possible especially on that vintage unit.
That side rear area will generally get warmer than ambient temp. Most will have some type of insulation there, fiberglass non-combustible, and heat shields.
J & J
+ Kickr's the Vonderhund
, ES-38RSSA, 19.6K#
, 3500HD-Max, CC, 8'-DRW, 9.1K#