I ordered the wall mounted battery bracket through the company that built my trailer. You can get them however through
Summit Racing for example or even on
Amazon. Just do a search for "battery boxes and trays" and then select the one that fits the deep cycle battery that you will use to power your winch.
I put the battery in a plastic battery box to give it a clean look (and to contain any leak/residue that might form on the battery), but it still allows easy access to the battery terminals to hook up a battery tender. My battery also powers the LED strip lighting that I installed along the ceiling edges (the LED lighting power leads are buried in the wall and exit the wall in back of the battery box).
Here you can see where I mounted the battery on the wall above the winch (and under the spare tire) in the front, V-nose of the trailer......with the LED strip lighting along the ceiling edges:
Brad in Maryland