I'm really interested in what you develop. I also have a problem lifting the 6 volt batteries into my battery box, which is in the front compartment. Like you, it's a physical challenge lifting them into the box while bent over, twisted around and trying not to get battery acid on my clothing.
To answer your question about the Trojan battery straps, yes the end hooks do slip into the plastic tabs (slots) on the battery top. They are much stronger than they look, I've never had one break on me. The problem is that the Trojan straps are a bit longer than the battery, and they "curve to allow a hand hold". For my application, they were a bit too long, so I modified one by cutting about 4" off the strap. Now, it's barely long enough, but there's not as much space between the battery and the winch hook. I barely have enough space for the battery to clear the upper bulkhead and the top of the battery box, but it does fit --- BARELY---.
What I finally did was drill two holes in the angle iron "framework" for the upper deck and ran a piece of 3/8" threaded rod between the two iron pieces. I slipped a piece of 3/8" tubing over the threaded rod ( to roll with the strap and to protect the strap from the threaded rod. I use a 1" ratchet strap attached to a hole in the pinbox to "ratchet the battery" into position over the battery box, then reverse the ratchet strap while holding it tightly and let the battery slowly lower into the box. It's worked fairly well, but I'd be interested in a simpler way to lift them in and out of the trailer.
Keep us posted as your work continues, I know of more than one fifth wheel owner who'd be interested !!!
Oh, Trucker Lou, a member here, posted pictures a couple years ago of his "pulley system"... I'll try to find that thread and post a link if I can locate it.
ADDED: The pictures of that pulley system are in post #26 here:
http://www.keystonerv.org/forums/sho...6486#post66486
The pulley system Trucker Lou devised wouldn't work on my Cougar, I don't have enough "headroom" between the battery box and the pulley support. What I did was use the pulley support (the round rod between the two blue side attachments) as a pulley and ran a 1" webbing strap over that rod and used that to lift my batteries. The webbing strap is temporarily attached to a bolt hole on the pin box and I just "ratchet up the battery" and push it into position over the battery box.