Remove the travel trailer fridge by finding the bolts or screws that hold it in place and undoing them. Unplug the refrigerator and unattach the propane line. Take the refrigerator out of the trailer. If the fridge seems stuck in place, have one person pull from the inside of the trailer while another pushes through the exterior access hatch.
Close off the propane line with a push fit cap or plug available at most hardware stores.
Slide the new refrigerator in place, plug it in and attach it to the floor by the same method the old refrigerator was attached. If this isn't possible, drill holes through the bottom of the condenser pan or the metal covering for the coils and screw it into the floor or wall. Install a newer refrigerator with a rear condenser and coils because it will use the same vents as the old fridge and not require any extra aftermarket fans to stay cool.
Read the owner's manual to see if extra ventilation is needed if you buy an older-model refrigerator. If it does, wire a small fan, such as a computer fan, to the refrigerator's thermostat so that the fan comes on when the compressor runs. Install the fan in the back of the fridge enclosure.
Finish the space around the front of the refrigerator with decorative trim that matches the travel trailer's decor. This has the added benefit of holding the fridge firmly in place.