This year will be my 11th Burn, and with the exception of the first year, I've brought an SLR camera Film in 2002, 10D in 2003, 20D in 2004-2008 and D5 Mark II in 2009-2010. First things first, I never once, not even for a few minutes, walked around with my camera out of my bag unless I was shooting. Now that doesnt mean I didn't keep it out for extended periods of time, but the camera had two places, either in my camera bag, or in my hands or on my tripod. Having said that, I have absolutely no fear what so ever of shooting at Burning Man. I shoot in the heat of the day, in the cold of night, during calm and yes, even during intense dust storms. In fact, I love shooting during dust storms. Some of the best stuff I've done in the last few years has been during intense dust storms.
Also, please note, you asked an question that is important to discuss. You referred to your cameras are "Dust proof". There is no such thing, especially with SLR cameras. Playa dust finds its way into everything! The 5D MKII and 7D are both incredibly well sealed (although I believe the 5d is a little better in this area), so you have that going for you. But the concept of a dust proof camera is along the lines of perpetual motion. Just not possible.
Here is what I do:
1. I carry my lenses, camera and accessories all in one somewhat inexpensive, and Burning Man only, camera bag. I typically get 2 years of life out of said bag, and I never spend more than $30 on it. I like the canon 200EG bag. I wash it in the laundry machine when I return. I am very hard on this bag, and hence, it lasts no more than 2 years out there.
2. I ALWAYS keep a lens cap on my camera unless I'm shooting or composing a shot.
3. I change lenses all the time. I do it quickly, and I try to avoid doing it with dust, but I've changed lenses even during dust storms when I REALLY needed a different lens for a shot. I carry ONLY L series lenses which have better seals and weather protection.
4. My camera stays in camera bag until I'm ready to shoot with it. Yes, taking it in and out of the bag as needed is a hassle, but this is the most important aspect of keeping your camera clean and safe. I cannot stress this strongly enough.
5. When I return from Burning Man, I tear open my bag, and spend hours cleaning everything. Lenses, filters, accessories, EVERYTHING.
6. I shoot with a 5D Mark II, and I don't trust myself to clean the sensor, so I take it to Samy's camera and they clean it for free (because I bought it there). Unless you truly know what you're doing, don't try to clean your sensor yourself.
7. When I bought the camera, I bought the warranty that includes coverage for accidental damage, and I have an additional rider on my renters insurance that covers all of my camera gear, including accidental damage. This is incredibly empowering, and makes me feel safe about bringing the camera out to the event. But even without these layers of protection, I would still do everything the same way. I would not fear using my camera. You bought it to use it, yes?
8. I do put a protective cover over the LCD displays (the top black LCD and the rear preview lcd.). Thats a no brainer and costs only a couple of bucks.
9. UV Filters are put on prior to Burning Man, and never, under any circumstances ever come off out on the playa. Once you scratch a lens, its toast, so I never ever let the face of my lenses touch playa air. Granted the rear elements get exposed when swaping lenses, but thats a risk I'm willing to take.
Here is what I don't do:
1. I don't keep the camera wrapped in plastic, nor in any kind of protective shield that gets in the way of getting a good shot. If you take proper precautions this just isn't necessary for either of your cameras.
2. I don't touch the camera with dirty hands. If you've been before, you likely know the difference between playa clean and clean and I don't touch my camera with playa dirty hands.
3. I do not ever, under any circumstances, put the camera down anywhere unless its in the bag. It never hits the ground (unless its in my hand for a low angle shot), and it never leaves my sight.
4. I never ever hand my camera to people I don't absolutely trust. You don't want to be in a situation where you have to hold somebody accountable for destroying your camera. They may be your best friends out there, but Burning Man tends to lower peoples guards, and you just never know could happen.
I remember something I'll never forget from 2009. I was sitting in center camp, drinking a coffee, and a guy sits next to me holding a brand new Nikon Camera with a pricey lens attached. Easily a $2,000 rig. Now this moron had no camera bag, and this camera was bare. It didnt even have a lens cap on. It dangled from his shoulder, and he even knocked it into the bench when he sat down. Now this guys hands looked like he just rolled his them on the playa. He was flipping through pictures he had shot. Holding the camera with filthy hands, he noticed the thick layer of dust on his uncovered lens, so he licked his thumb (I'm not making this up) and briskly rubbed the front of his lens doing nothing but making mud. I wanted to intervene on his cameras behalf, and yank the thing out of his hands, and care for his camera properly. Alas, this camera already have a lens in the grave. Its likely this jackass didn't have
My point for retelling this story is multiple fold. 1. An idiot will find a way to destroy their camera on the playa. Don't be this douche. 2. Not pretending the ground is camera lava will invariably result in a destroyed camera, and lava hands can be just as hazardous. 3. If you just don't care about the camera, and have that kind of money to throw away, feel free to be brutal to your camera! You'll destroy it in no time. 4. Respect your gear, and it will reward you with years and years of great images.
Please note: I accept no responsibility for what you do to your camera based on my advice! But rest assured, I've spent a decade shooting countless images on the playa, and these simple tips have served me incredibly well. I've not run into a single problem related to gear other than a batter grip that failed in extreme heat. But it turns out there was a recall on that one, so that was Canon's fault.