We have been using an old toolbox with a little GEL cell and some LED lights for a while (See details here). Its only a little thing but the double handling of getting it in and out(the point of a camping trailer is to reduce this) and having a bit more room to pack stuff you don’t need), and remembering to get the solar charger out is a little tedious. Then there was the time, despite our use of camping lists we left it at home completely. Anyway here is version 2. Basically a little hardwood plywood box on the side of the trailer to keep all our stuff in. We opted for hardwood, because it seemed like a good idea. I had the folks at bunnings to most of the cuts (only $1 a cut and they don’t usually charge) so that it would all be nice and straight when screwed and glued together. A piano hinge, some self adhesive door seals and some left over house paint (gun metal grey) and it doesn’t look too shabby. I’ve made up a few more lights using the LED strip lights for inside and out. They are really light (as in not heavy) so just attach to bits of velcro on the various poles around the trailer. I’m using the same battery (7AH) from the tool box, a $2 voltmeter from eBay to keep an eye on e the charge. The solar cell I’ve screwed to the top of the toolbox (hope no 0ne steps on it) so it trickle charges away in the carport and on the road and have routed the cable through with the other power to the trailer.
Inside i keep the torches for the toilet runs (and some times it is with little kids) and adapters to charge the mobile and the Kindle as well.
All in all I’ve still resisted the urge to spend lots of money, over complicate life through developing a great engineering solution thats fiddly. Plenty of room in the box if i decide for bigger batteries down the track, charge controller etc..