D800 body armor
I can't answer for the D800 (don't have one, can't see that I need one, my D700s still work just fine, tyvm), but my V1 shuts down if it thinks it's getting too hot. Note that this has only happened once, when I was doing a lot of continuous video and stills at a concert, with the V1 held in my hand. It gave me fair warning, when that was ignored it said goodnight. After a few minutes of cooling (I removed the battery and SD card and blew gently into the recess to help shift heat away), I hit the On button and away it went. No ill effects have shown up, and that was over a year ago.
I have to agree with the previous poster though - camera armour is mostly something that is designed to separate you from your money. I have carried cameras all over, dropped more than a few and without exception, they are still going fine. A decent lens hood is probably of more 'protective' use than some dodgy bits of cast urethane. Besides, it looks really tacky... As always, you are free to think differently. Enjoy your holiday.
It's no longer about the gear; all of it's good, and most is better than our skills warrant. Go and learn the craft, learn to see the art, and make fewer, better, photographs.
Seriously, it's NOT about the gear any more.