maxxair just called back. He said it was most likely that the board was burned out by my converter. He said a regulator would definitely be helpful for my system. They have an updated board they are sending me that can withstand 13.8v but the regulator would be a good idea to protect it in the future. He said it would be good to regulate the input to 12.4v. The callback today was really fast but it may have been a follow up from yesterday's call, not sure. I think if I would have just been using my stock converter and FLA battery I would not have had any issues (I don't connect the truck to the slide in camper at this time).
So, very helpful support/warranty service from maxxair for sure. I should have suggested they list the input voltage limitation in the installation guide to help others but it sounds like they are aware of the issue. If you are looking to get a maxxfan maybe consider you will need a voltage regulator if you use a high output charger/converter that is specifically designed to work with LiFePO4 like I am using.