As always I am doing research and have been wondering about this type. One hole no screws...I retrofit similar on my boat trailer cause the square surface mount type were always getting broken, just in a bad place to get knocked, so these have been on for a couple of years and still fine.
Used on boat trailerThen I saw these as well similar.
Chrome bezelON the Lance the back markers are mounted on a metal overhang reverse cant flashing effort along with the high intensity back up lights...don't expect any leak issue here for lights, may be others associated with the metal bit...will not know until removed...also the TC was wired for Back Up Cam, wires should be there too.
METAL OVERHANG


Before you ask: The air deflector keeps the back very clean, even in dust and snow/slush conditions. They are not made any longer, with the poor economy of the last six years the company found that not enough extra funds available from folks that had buses, their main client. Too bad RV folks didn't offer as an option.
Back to lites...ONE HOLE even if it is bigger...the whole circumference is visible for inspection, no hidden screws and wire hole...since the TC is getting a rebuild then a prepared mounting spot for this type could be made easily.