I went the cheapest and easiest way and used basically reflective bubble wrap. I forgot the actual name. I also used spray foam for the hard to reach places. Ideally I would use spray foam for everything if I was starting over. I winter camp in my van and my mr buddy heater is more than proficient. Even just body heat keeps it warm in there. Id worry more about sound, 4 am plow trucks can be annoying when parked at a ski resort.

Whatever you do use. Make sure it can't get moldy. Battling condensation is tough. Especially if you have wet gear drying in the van. Ie. ski stuff or a dry suit. Make sure to have vents and a fan for airflow. Even if heat escapes a little it's not a big deal because it's as small space. A 20lb propane tank lasts me all winter when I run the heat in the evenings and morning.

As far as keeping it cool goes have good reflective shades for the windows. And air flow. I don't have the funds for a sports mobile but my dad has one and it is pretty amazing. It's comfortable pretty much in any environment and everything is user friendly.