Are cargo trailer door locks even designed to open from the inside? Forgive my ignorance.
The OP is asking about a classic 1947 Tourette teardrop, it's not a cargo trailer.
To address the question, I haven't solved it yet in my trailer, so I've got this 30" square of un-insulated aluminum in the side of my cabin
I'm thinking of abandoning the foam insulation for the door and going with a thin piece of wood covered with the hull liner that the rest of the interior is covered with. No R-value, but better to touch than a slab of cold damp metal.
<Chas>