Well, you could number the panels like spaces are named on Navy ships. It's more complex than is needed for a trailer, for example an Airstream will only have one deck.
Deck number is usually the first part of standard naming scheme.
Next is frame number. Name the panels for the frame they attach to on their leading edge. First frame is 1; space ahead of that is labeled 0. Increase the frame number by one as you go back frame by frame.
Ship spaces are numbered from the keel, or the ship's centerline from nose to tail. The compartment numbers increase as they go outward from the center. Spaces on the port side, the left side when looking forward, are odd numbered; spaces on the starboard side are even numbered. You can number your panels odd for left and even for right after the frame number.
You don't need to worry about the compartment usage code letter. Or you could use it if you enjoy the nerdiness of it.
You can google them if you're curious.
Have fun.
Scott