Its a good idea to insulate the doors
Good advice above; I did notice on side and rear CT doors were made with many holes at cuts and welded joints these really benefit from being filled with spray foam and caulk; also I wished Id filled the inside of all tubes with spray foam; you'd get little if no sweating that I get where the metal cold bridges from inside to out.
I used 1" pink hard foam insulation (or was it 3/4? whatever max would fit) friction fitted; and covered with a single piece of 3/8" ply screwed to the square tubing door frame; all edges of the ply need to be sealed with a waterproof finish (I use varithane) or water will wick into the ply on exposed cut edges when wetted.
also take a file or grinder and round off (chamfer) all outer edges of the doors so they don't cut tarps, people, pets, clothing and equipment.
Happy trailers; cheers bc Dave