increased insulation for refrigerator

Thanks for the replys. I understand reducing the space around the sides of the fridge, so would it be best to use the styrofoam sheets or just make the compartment smaller using something like plywood? Seems like the styrofoam would accomplish both space reduction and insulation and be easy to work with.

In either case the fridge will have to be pulled. If just adding insulation then the flame retardant engine firewall insulation sounds like a possibility.