I had the same issue on WFCO panel on a previous trailer. I used a small sheet metal screw to hold the door closed. It's usually pretty seldom that the panel needs to be accessed, and only takes about 10 sec to remove the screw.
if it is the typical WFCO panel, and it won't stay latched it's probably the latch pin in the door. Those are avaiable as a replacement part, most any RV shop should have them, if not amazon or ebay probably has them. I had one break on our 2011 Outback and easily found the pin online, but don't recall where it was.
You may be able to replace just the little latches that are supposed to hold it closed. The little square quarter-turn plastic gizmos, for instance, are readily available and just kind of snap into their hole in the door.
A carefully placed magnetic catch (or just a magnet) might work nicely, too.