Interesting, I've just looked into the weather here. We get about double the rainfall, spread over about 40% more rainy days. Our record maximum and minimum is 44°C (111°F) and -6°C (20°F). We're in a relatively cold and dry area. We have no where near the altitude of the Rocky's, the highest mountain in Australia i only 7,300', we obviously have a lot of outback and heat though in other parts.
I had a hard lid rooftop tent for a while. It was terribly cheap and dodgy, but I loved it until it broke. Even hard lid rooftop tents are only just starting to take off here, 90% are the ARB style flip over ones, which I agree are basically a tent with a ladder.
I've looked into making panels, I do have some (limited) experience with composites and could probably do it acceptably. But there are a few good companies around who specialize in making and cutting panels for custom trailers for fairly reasonable prices, especially for something this small. The accuracy, quality, flatness and speed are way too appealing for me to bother with DIY. Plus I'd have to buy a vacuum pump, a router, make jigs to cut it with etc. Their thickest panels are around $150-180/m2 ($10-12USD/ft2) already CNC cut to shape.