Things are done like they are for a reason.
The tents are air conditioned with diesel-powered ECUs because people get heat related illnesses when they are not. They aren't kept at 68 degrees F - more like 80-85, but it's better than 105-130F outside. The ECUs also act as heaters in mountainous environments - Afghanistan, for one.
A TOC (command post) is a tent complex surrounded by concrete barriers and/or concertina wire. It's powered by generators. The wire and barriers are to stop potshots from firearms and to offer some protection against mortars/grenades/rockets. The wire isn't intended to harm, it mostly sticks to your skin and clothing and prevents you from going inside the post. The generators are used because they fit inside the perimeter.
Reflective blankets aren't used because the reflective blankets stick out like a sore thumb from the air, or the ground.
Insulation is not sprayed on the tents because they, you know, move...
Solar panels - envision putting a solar panel outside the perimeter. Envision carrying around solar panels and setting them up where you operate. Impractical from a logistical standpoint and could not be secured efficiently against attack without extending the perimeter to perhaps double or triple the circumference, with all the associated costs in additional manning for force protection. A nonstarter.
The same arguments apply to LSA - the places soldiers live - but with some modification. Some are fixed and might be amenable to alternative power sources, but the perimeter guard issue rears its head again. You can't beat generators for portability.
You were on the right track with the thermostat but then you went off course after that. Reflective blankets are actually used in our tens, under a layer of tan fabric. The tents are actually very energy efficient. Solar panels are not really an option as regularly occurring dust storms or indirect fire would regularly mess up the solar panels, and would be a logistical nightmare. Tents that are to remain stationary are regularly foamed, not only because of the insulation it provides, but because it also keeps the high level of dust outside. This is a link to the types of tents and ECU's we use: http://www.alaskastructures.com/
Our business in life is not to succeed but to continue to fail in high spirits. -- Robert Louis Stevenson