Check to make sure the cooling fan at the top of the fridge is running, and check for dust accumulations in other areas that might impede the necessary air flow. If you'd like manuals for it, go to www.thetford.com, and select the model closest to yours. It should be similar to the model you listed.
If my answer helps you, please click on the 'accept' button. That's how we experts are paid for our efforts.