I also use the half-turn-past-hand-tight method. But instead of a screwdriver, which I used to use, now I use an open-end wrench that's for the jam nut. It fits well in the turnbuckle, and then I can also use it on the nut. I put the wrench in about half way, and can turn the extra 1/2 turn by twisting on each side of the wrench. It clears the camper and truck fairly well. One of them I have to tilt the wrench so instead of 90 degrees to the turnbuckle, it's more like 45 degrees, but it's still easy for this wimp to do the half-turn.
I've had the turnbuckles almost completely fall off once, and get very loose another couple times. But the jam nut has almost eliminated any problems. Almost. Once one of them came loose about halfway across the Mojave Road, a several day trip. But the other three were still holdin' great. The jam nut (which didn't come with the installation) has worked quite well, in general.
I flipped the turnbuckles so it's easiest to get to the jam nut. To me it's obvious if it's righty-tighty or lefty-loosey-backwards-I'm-cornfused because one way is obviously tightening.