The interior panels to the left and right of the door were simply crudely bent sheet-metal that filled the gap. I didn't meet my OCD standards 
So I got a couple of panels cut, which I then marked and cut holes all through, and they were then bent to fit the profile.
I butchered the cut-out on the top right; it's an opening to fit a 110V outlet, and I wanted rounded corners (because of my OCD). Of course I didn't use a step drill, and the large diameter bit I used grabbed and tore it. Lucky it's hidden once the outlet trim is fitted. The middle clump of holes in the same panel is for a fuse block, and the bottom four vertical holes are for various 12V plugs, I have a switch for the inside lights, 2x 12V outlets, and a dual USB outlet. The panels were installed with self-drilling screws.
You can see the 100V wall box behind the top cut-out; it mounts to the panel using the screw holes that would normally secure the outlet to the wall box (eventually the guts of the outlet will also use the same screws). I used an old galvanised wall box I had lying around from some previous demolition, and had to cut a small angle off the corner so it clears the inside back steel structure of the trailer.
The panel on the other side is a single 12V outlet for our cooler and the master switch for the 12V converter.
I also started installing things so I knew where to run wiring. The light on the door services the kitchen area; the wiring will get covered in expanding mesh tubing later.
Once most of the panels had been fitted out, it was time for the AC-->DC converter. I had thought about using a proper RV 12V power converter, but then realised I could go down the DIY route. I had a decent 12V power supply from a PC sitting unused in a box. Specs:
When I measured it, it put out a constant 11.9V. Close enough for me. Not quite the 12+ volts a good battery puts out but I doubt I'd ever notice the difference. Plus it was free (!), small, and has more than enough power for my needs. All we wanted to run was a small eutectic cooler and some lights - I'd be unlucky if we draw more then 2A.
Opened it up and got to investigating. It has a main switch on the reverse but is actuated by grounding a low voltage (~2V) wire. I decided to use this wire as the master on-off switch next to the door that I mentioned above.
There are a multitude of wires, but only 3 different voltages: 12V (yellow), 5V (red) and 3V (orange), while black is ground. These wires run everywhere as they are designed to connect to various components inside a PC case. Most are generally unused.
I thought about de-soldering the unwanted wires, but it was such a mass of solder on the circuit board reverse that my little soldering iron didn't stand a chance. Instead I cut back all the red and orange wires and covered them with heat-shrink tubing.
That left just a few 12V and ground wires remaining. I elected to use 2 yellows to supply the power to the fuse panel along with 2 black wires for ground. The remaining yellow and black wires I coiled and secured out of the way in case they are ever needed for more capacity later.
Put it all together and tested the cooler overnight. Below you can also see the grounded green wire to keep the thing running. Success! Now I just had to find a spot to mount it.
Then it was time to mount the converter. I had intended to mount it on the vertical back piece of ply above the little battery storage box. However, the PC power supply doesn't come with handy mounts for that purpose plus it would block the storage cubby somewhat, hanging something above it. I found a nice spot at the front left corner of the trailer.
The trailer wiring and AC power cable come through the floor here so it was an ideal spot. And it fit like a glove (as if I'd planned it, which I hadn't) between the two shims you can see poking out from below the base edges (the floor was not very flat).
To secure it in place I came up with this:
A little wooden bracket to clamp down on the top of the unit. It sits on top and is screwed in place through the side of the drawer unit base.
It includes a little gap to accommodate the 12V wires you can see above as well as the incoming AC power. On top I placed a 3-way junction box I found online for about 6 bucks that even included a terminal strip inside. Not sure how we survived before the days of Prime shipping... The junction box was needed to terminate and split the 110V incoming into 2 destinations (the 12V converter and the 110V outlet on the inside back panel).
Here's it sitting loosely in the intended position:
Time to finish this write-up. Really all that's left to do by this stage is finish the wiring and test it.
I added an extra hole and grommet in the junction box to handle the 12V wires. I used the junction box to terminate a couple of 12V wires and make 3 connections for 110V AC wires.
Wiring in progress. To run the 110V to the outlet I purchased a short extension lead and cut both ends off. I am using 3 of the 4 terminals and fuse holders so I have room to add 1 more circuit if needed.
The finished panel:
Coming together:
All buttoned up and ground wire (yellow) connected:
Time to see if it all works. The LED strips lights work - I put one above the inside of the door and another two-thirds of the way down the length of the inside.
This one gives you a better idea of the finished product:
So stoked with the end product! Just a few more things to take care of:
I need some stabilising legs for the rear as the trailer tilts easily. I'm hoping to get a couple of wind-down legs, one for each back corner.
I also need to do some modifications to the trailer to make it legal down under. My family and I are moving to my hometown in Australia for 2-3 years with the company I work for, and I want to use the trailer there as much as possible. I need to add amber indicators to the rear, fit some flexible mud flaps (the mudguard trailing edges are too high off the ground), replace the vehicle wiring connector to a 7-wire system, and replace the coupling to one that meets Australian standards. I also probably need to fit a braking system as trailers there need to have brakes if they are rated for more than 750kg/1650lbs. These mods can wait until after we arrive (whenever that might be with Covid and related global shipping issues), but I'll try document them if they are worth sharing.
To enable the 7-wire connector system, I added a junction box underneath the trailer. The idea being that I simply replace the short front section of the wiring between the vehicle plug and the junction box and leave the rest of the wiring untouched.
Thanks for following along!
