Rec-Pro has a "custom size door" availability. You can order doors in any size you want, to the 1/2" measurement.
https://www.recpro.com/custom-rounded-rv-baggage-door/
There are several other sources that provide the same service in "custom built doors".
Keep in mind that the corner radius is unique to the door and has to fit the opening in YOUR trailer. So, I'd get the door "IN HAND" before cutting the FILON opening in the trailer sidewall. That way you can "custom match your opening to the custom radius on the door".... Otherwise, you stand a 50/50 chance of having "sunlight at the corners when the door is closed"....
Whatever you decide to do, make certain that you're using the same measurements as the door supplier..... If you're measuring the opening on the trailer and they are measuring the opening on the door frame or worse, the outside measurement of the flange, then you stand a chance of ordering a door that could be 1" too big or 1" too small. Make sure you and the supplier are both talking the "SAME MEASUREMENT LOCATIONS".....