Thanks, I just changed my order from the cheaper buck converter to this model that will work for up or down. Went with the 25 amp unit ($60) since it will cover the 5 amp fan and 8 amp fridge (the 120v heat element doesn't work on my fridge so I will be running it off converter while on shore power and propane when on battery, until I get around to replacing the 120v heating element).
25 amp should be plenty since the original "converter" (which was just a transformer that made a lot of noise when in use) was only rated at 9amps. This will simplify my installation as well. I was going to go with some relay/solenoids and wire those into the original electric panel that had a converter/batt/off switch to isolate things but now I will just wire the converter to the battery (via my disconnect plug) and the converter through this regulator to the fuse box. Then I can run shore power while charging my battery if I want to. When on battery only, the converter will be powered off but the battery will flow to the fuse box via the converter outlet lugs.
EDIT: Still waiting on warranty callback from maxxair. I recieved a callback from the tech support line yesterday after about 3 hours, and they immediately transferred me to another hold queue after telling me I needed to start a warranty claim and was in the wrong "area" for warranty claims. I called back today and was added into another hold queue. There is one person that does warranty according to the person who answered the phone today. There is no direct number or option to get to warranty claims, you have to wait on hold until a support person picks up or calls you back, then they transfer you to the warranty person which puts you into another hold queue that I was told is running about a day behind! Hopefully they call me back this week. If they don't honor their warranty I will just put a reversible variable speed motor controller on this unit and be done. It is beyond the return date and amzn sells the controllers for much cheaper than a new controller circuit board from maxxair. The motor controllers are most likely more robust as well, I think they are rated to operate up to 36v. I will still be putting the regulator in to protect any other 12v devices/appliances though.