It'll have a hook at its top (as shown), and a shackle to replace hook shown at bottom.

I'd really like to find a highfield lever or truck load binder of a suitable size. No luck as of today. (That lightweight slack chain is a safety to keep boat from sliding backwards off trailer.) Pls. let me know if you are aware of a source for a suitable chain tensioner.

The intent of the new D-ring and heavy chain is to avoid situations like these:

   

BTW, this is the way an anchor for a rear tie-down strap has been provided -- by me, not the trailer manufacturer. Adding this feature dramatically changed the "feel" of the trailer while driving -- a vast improvement over the trip back from the trailer factory.

Another BTW, those small black fabric tie-downs (like the one shown below) are about worthless. They really are dangerous, because the "over-center" tensioning buckles can easily bend the "axles" within the buckles. In other words, they are self-destructive, giving the user a false sense of security who may not realize their serious weakness.

In the photo above left, the heavy chain is shackled at the D-ring. I tried pinning the next link up, but could not.
Dilemma: How to snug up the heavy chain, yet have the ability to loosen it if the boat travels forward during travel? (As it will during braking.)

Photo on right above shows how it is today.
The black strap is poorly designed, and its application here is kinda klutzy, IMO. I think I can eliminate having to deal with two hooks -- one at each end of chain when launching and retrieving the boat.

I've acquired a "500 lb" "ratchet strap" (strap is 1" wide) with a well-made ratchet device. (Brand is SmartStraps.) I intend to mount the new device between big hook (on chain at top) and bottom link, next to shackle (on chain at bottom.) The straps will be connected to chain using shackles, not hooks; their big klutzy rubber-coated hooks will be discarded.

So the chain, with its tensioning strap will come off in "one piece" and will serve two functions:

1. Keep the boats bow off the rubber bumper.
2. Hold the boat snugly to the trailer when tensioned (up to 500 pounds), and
3. Serve as an emergency restraint to keep the boat from over-running the tow vehicle if tensioner fails under load.

(The tensioning strap permits installing and removing the heavy "tie back" chain without a heavy turnbuckle and the need for tools, etc.)

Well, so much for that solution. After towing the boat (to Wisconsin, Table Rock Lake and Carlyle Lake) using this rig, the strap failed:

For now, (11/5/12) I'll replace the broken strap and use this rig for my trip to Florida in March.