For the tongue box I used a Contico Jr Pro Tuff Bin. I have room for the battery, charger, tools, 12v circuit breaker, cutoff switch, and there is also room for some tools and my wheel chalks. The box has two padlock brackets so I can secure it while we are on the road.
I attached the tongue box with 3/8″ bolts mounted to 1″ square steel tubing mounted across the tongue for support.
I purchased a group 27 marine battery, which should be good for around 100Amp hours and tested the fit in the tongue box.
I cut the tubing to the proper width with a grinding wheel. I needed to make sure it was wide as possible to support the box and battery.
Here is the waterproof wiring connection from the front of the trailer to the tongue box. I am using some conduit and hubs to make it water tight as well as butyl tape and 3M 4000 under the screws and for caulking around the edges.
The view of the wires where they enter the tongue box.
The tongue box with the battery and board mounted master cutoff swtich, 30A circut breaker, and 2 amp battery charger.