Speaking of windows… not only do they contribute to livability, but glass is superior in terms of resistance to heat flow (R-value) and thermal conductivity (U-value) to the typical metal siding of a van.
If my Googling has served me well, I am calculating that glass has an R-value that is about 77 times greater than steel (for reference, Expanded polystyrene (EPS) rigid insulation is 1200 times more resistant to heat transfer than steel). Glass weighs less than steel, too. About 2.6 times less, for the same volume.
And of course, you can see through glass.
My shuttle bus conversion is on a Turtle Top Van Terra base, which has windows all the way around the cabin space. I hope to be able to open it up fully to take in all the views and the light. Or, if I need privacy and/or insulation, I will have multiple layers of window covers, blinds and curtains to box myself in completely, or provide privacy with some light still getting through. Flexibility is key for me.
I debated long and hard about vehicle selection and windows. In the end, I figured that glass is better than steel for my needs, even without the benefits of livability.
And yes… I am taking almost everything in my conversion this seriously (and empirically). Does anyone want to know the “R-value to weight ratio” of common van conversion insulation materials?