Absolutely the more windows (low insulation factor) on a given surface, the more the heat transfer (in or out) will occur. My point is even with a lot of windows, the wall insulation value plays significant role in overall temperature isolation, so I think manufacturers should share the R value of their walls, floor and ceilings. As buyers, we can take window surface area and other penetrations into consideration, but at least knowing the envelope wall panel R factor is an interesting spec that manufacturers should be able to provide. Same with pop-up softwall material which can very even more from manufacturer to manufacturer. The panel (or soft-top for that type of camper) R value may not be of much consequence for the average buyer's temperature use case, but it should be easy to provide so why not.
There are trade offs to consider, of course, with going with panels with higher R value and those tradeoffs may not be worth it for some manufacturers or the intended buyer audience. If AT Overland is prioritizing light weight for the AlterraXL, which I suspect is the case, then the walls will understandably be thinner with correspondingly lower R value. For the average user, it very well may be a reasonable design choice since from 30F to 70F, it won't make a significant difference in comfort or heating/cooling energy use. And, for those that operate at more extreme hot or cold ambient temps, a little more energy use (more propane to heat, for example) will compensate for lack of insulation while still enjoying significant weight savings over thicker panel walls. Or, for those that regularly camp in outlying temperatures (a lot of winter camping for example), they may choose a different camper all together.
We use our OEV Camp-X pop-top down a fair bit below freezing and are amazed at how little propane it takes to keep that pop-top camper comfortable. OEV claims R-8 walls and R-4 pop-top. Curious the R value of panels used in the AlterraXL. Maybe AT Overland determined that thicker/heavier panels were not worth the trade off in weight. Would be interesting to hear their design philosophy regarding that decision.
To make any comparisons, and simply because it really interests me, I'd love to see data on the total weight of ONLY the current AlterraXL panels and know their R-value. Then, see the overall weight of several thicknesses of thicker panels and their R value. Just curious if, with these particular panels what doubling or tripling wall thickness would do to overall weight and panel R value. Not sure if those increases would be linear or not. If so, then knowing current panel weight and R factor, we could simply multiply overall weight and panel R value by 2 or 3 if the panel thickness was increased by 2 or 3 times. Would doubling panel thickness add 50 lbs, 150lbs, 400lbs to the overall camper weight? I have no idea.
As noted, windows and other envelope penetrations are a factor to consider. One could measure and calculate the ratio of insulated panels to window to understand and compare different camper models. Same for selecting optional windows, as some campers offer, to understand the change in panel/window ratio.
In the end, I'm more interested in panel R values and weights simply because it's interesting to me. The panel R value isn't of much impact for the real world use in the average temps we camp in (25F - 70F). And the handful of times a year we camp at temps much cooler than that, we can easily burn a little more propane without carrying a lot of extra weight around the rest of the time. I want both high R value and low weight at the same time! but we can't always get what we want. Ha. If I had to rationally choose, for our use, light weight is more important than R value.
[Edit: If I'd waited a couple more minutes, I could have just said "x2" to what
@IdaSHO said. Ha. ]