On my T3-C trailer, I mounted the license plate on the rear tailgate. I got a rubber license plate bumper, put the plate in the bumper, and then mounted the bumper and plate on the tailgate. I could not figure out a way to get power up there to run a license plate light off the trailer lighting, so I just took a solar charged battery-powered deck light and attached it to the license plate. I cut the top off a steel license plate border bracket, welded a plate to that bracket, and then attached the deck light using some industrial Velcro to the plate. Light has a sensor on it which makes it only come on at night. It charges the battery the rest of the day. Works perfectly. HTH.
On my M416 I didn't want to drill any visable holes because I do not think it ever had a license before. I drilled two holes to the bottom on the back and bolted a piece of angle iron so I had a flat surface to bolt a early 40 series license holder. Could snap a few pictures if interested. I fill the trailer with water and does not leak with the drains closed. Drilling any holes that could possibly leak was not a option for me.
Id like to go middle bottom of the tailgate, but may need to occasionally run it without the tailgate. On the rear frame sure seems low and vulnerable. Anyone mount it in “portrait” orientation on a fender?
If you have a tailgate then mine wouldn't work for you. Here in AZ we have a option of running motorcycle size license plates on our trailers. I went this route on my car hauler. Went to a motorcycle wrecking yard and picked up a bracket with a light. Went this route because on the back they tend to get damage hanging below the frame.
That's pretty much what I did on our M101 CDN. I used 2 LED license lights above it pointing down, with a angle iron protection bar above them. The angle iron also has some shaping around the protrusion of the rear interior tiedown that lets me hook a bungee cord to it.