You are correct that trying to put the carabiners on by using their latching mechanism would have been too hard since the roof line is so high up, but worse would have been trying to unfasten those carabiner to get them off of eye hooks. It is much easier to slip the carabiners over the cut off eye hooks.
And speaking of that: I have found that the motion to put them on and take them off is more of a pushing motion. I use my hook thingy to push one side of the carabiner over the open hook to put it on, and then I must again use a pushing motion to move the part of the carabiner nearest me back over the hook.
I also have thought about one over the rear door, but I am not sure on that one yet because of the lines and door clearance.
If anyone has done that, I would like to see pictures:)
Del