I wasn't sure about carrying my gear either. I have an F-Stop Guru (which is great by the way) but it's too big for trail running. I wish F-Stop made a smaller minimalist pack with hydration with room for only one pro DSLR and a nice wide angle lens. Here's to hoping. I ended up using an old Mountainsmith fanny back, (thanks Yves!) with the shoulder strap to carry my D800 with Nikon 14-24mm fatty wide angle, some spare batteries and snacks. I added stability to the whole package by using an F-Stop Gatekeeper strap around my front to pull the Mountainsmith shoulder strap snug. It did surprisingly well. I have tried a LowePro toploader for this but it is too bouncy on the front. and not made for the back.
I am not sure what model it is but it most resembles the current
You can see the strap that came with it on my left shoulder.
On the Mountainsmith website there are smaller ones that are probably more appropriate for running.
At the beginning of our run I ran in back as any newbie to an area would do in a group. When I came to some pretty sections I would holler out to Ryan and Josh to come back and run it again. They were sure nice about it but I began to see that this was not ideal for either one of us. It breaks up their run and I get less shots because I feel guilty asking them to stop all the time.
After a bit of this I decided to run with my D800 in hand with the lens cap off. Quite scary really but the terrain was not too technical. Once I did this, I ran ahead of them and whenever I came to a sweet spot, I would stop and shoot a bunch as they went by. I would then have to pass them again which I am sure was a little annoying, but perhaps not as bad as having them run up the same hill twice. So although I was a little nervous, I was able to get some great shots without having to ask the subjects to "do it again".