I don't have much info for you, but figured it would be better than the nothing you receive so far.
After you have done all the calculations and finally decide on the size of your battery power system, just go ahead and increase that by 50%. Probably more considering your location. Or add a small wind generator to supplement the solar. Maybe it's just me, but in my experiences, those calculations don't hold up for long once the batteries start degrading a little.
Burying the batteries should definitely help with the heat, but something about that idea just doesn't seem quite right. Might not cause any problems, but would be more of a hassle if nothing else. If you have decent batteries then a sun shield over the cabinet is plenty of climate control. Next time you drive out to your tower, leave engine running for a few minutes with the AC on full blast. Then go pop your hood to see how hot your car battery gets.
Without knowing any details of the wireless link it's kinda hard to make recommendations. I don't have any experience with the bandwidth requirements for that setup, but I'm sure you could probably save about 40W by using a Mikrotik radio. And with the money you save using Mikrotik you could probably double the power system equipment.
And you probably already know that "Long Range", "Camera" and "Mounting on tower" don't mix well. Hopefully your tower doesn't have much movement, you have a solid mount, and camera can handle the extra movement. Even if that all goes well, it's still a challenge getting a steady picture if you are 30x or more zoomed.
I wish you were in my area with that project. I'd offer to come help for free. I have done several PTZ dome tower installs, but have been wanting to do a thermal setup for a long time. If I ever get enough money to buy one, I would probably be to worried about mounting it on a huge lightning rod. Especially here in Texas. We usually get a couple years of service out of them before they die. So by then it's time to upgrade to the new model anyway.