If you have a standard RV refrigerator, the cabinet may benefit from insulation. Frequently this cabinet is just 1/8 inch plywood with little or no insulation and with upper and lower vents to the outside, temps on the backside of the cabinet are pretty close to outside air temp. I discovered this problem since the thermostat was located on the cabinet wall and it would never function properly.
Anyway, I pulled the refer out of the cabinet, found the factory insulation that was visible from the backside was just a couple of strips about 8 inches wide and 2 ft. long, totally ineffective.
I used 3/4 inch rigid foam board and was able to install a double thickness, first one set inside the framing and second one completely covering the framing. Also did the underside and back of the cabinet above the refer. This fixed the problem with the thermostat.
If I were lining the inside of other cabinets, I would use rigid foam board and NOT reflectix. Foam board does not require a dead air space and it works for both heat and cold. Reflectix is not really an insulation, but a mirror for IR rays. So it has limited benefit after dark and being metallic it is actually very conductive thermally. Attach it to a cold wall and it will still conduct heat from inside the RV to the outside.
Reflectix was designed to use in outer space where there is no atmosphere. But here it has limited value without a dead air space. You won't find it used in residential home construction. The RV industry uses it because it is cheap, light and they can claim and 'effective R value' even when they install it incorrectly.
Just my $0.02
