I believe the point of these trenches is to have them open for spring/summer/autumn and then cover them for the winter. Since the trees are kind of dormant in winter you shouldn't need to access them much, if at all. And the shade from the south wall also wouldn't be an issue in winter.
I assume they accessed them at the end via a series of steps or ramp that was also covered for the winter.
If the roof was really sloped at 30-35 degrees, then it would let decent sunlight in around the solstices. But the sketches sure don't seem to show them at 30 degrees.
I was looking up cold hardy citrus from
Mckenzie Farms and the Owari Satsuma sounds like a candidate for this. Good down to 12F. I'd imagine that tree in a 6' deep and 5' wide trench with a blanket of snow above it would easily get through my winter above 12F. I think...