I use the Fulltyme. It's basic, but it gets the job done. I carry a Radrunner and Radmission on it, I've driven probably 600 miles with it.
I'm paranoid so I use a ratchet strap from the top of the rack hook to my car's roof racks to take a little weight off.
I more or less do the same thing but I was able to use a old rubber coated lock cable and a strap from Husky to pull back, which pulls up a bit too. It takes a little weight off but most importantly it keeps the bikes from slamming up or down (it's the weight plus the leverage that I am "paranoid" about).
For me there was nothing to buy as I pulled out a few items I had laying around and it tuned out to be the perfect set up and SUPER easy, takes 5 seconds.
I'll take and post a picture next time bikes are up on the rack (it would probably only work if you have a rack very similar but might give an idea of what you could do as, like you, I think a little extra support is warranted).