winch mounting on trailers
I used a 3/16" steel plate mounted under the decking on my trailer.
Welded nuts to the plate so the winch bolts down thru the deck into the plate.
I put a couple of screws up thru the bottom attaching it to the trailer, so the winch is removable without having to crawl under the trailer.
I have a tool box on the tongue so it was my only option.