Motzy, I designed a method for internally venting heat from containers in case you want to use it.
It does use some space, but worth it in sunlight.
If I haven't said, I suggest that trailers should be painted for visibility.
Drivers tend to not see them anyway, especially the low ones.
Most seem to be painted black.
Who are they trying to hide from anyway?
I can only guess it's to hide bad welding???
I saw one for sale recently, all in black except for some reflectors.
You can barely see it in the photo, and it isn't small.
I just painted my new liner in gloss white and it makes a huge difference over plain plywood in visibility.
It should be possible to get useful light on the inside with just LEDs too.
I used an acrylic one part, as they told me it's the best choice for UV exposure and won't leaf.
I did use a lot to get it to go on smooth and cover well.
It goes on very thick and is hard to apply with a brush or roller.
I spent almost as much as getting marine grade wood, but it looks good and durable.
I have also used rustoleum HD aluminum on steel.
It could be used on wood, but it leafs a lot.
That isn't an issue on the outside, but I don't need it on the inside.
I recommend the 3M conspicuity reflective tape.
Usually 980 or a similar number.
Look for diamond grade, not the lighter stuff.
They make a vertical version as well as the more common horizontal stripes.