I will have to go get a good bar, I just broke my second one.
I bought one from an auto parts store for about $20, came with a lifetime warranty. I snapped it when trying to remove lugs from the road wheels that a tire shop had over-tightened. Walked back in and they gave me a new one.
If you still have the two pipes that came with the factory bottle jack the larger of the two will fit over most 1/2" breaker bar handles, but it's not as strong as a floor jack handle.
A real brute force option would be to jack the rear of the truck up, place a 2x4 under the breaker bar handle, and slowly lower the truck. At a certain point too much force could cause other problems - like bending the sheet metal of the rear door.
Chemicals and heat are probably better things to try first. Also, if you can get your hands on a roto-hammer you might have better luck than with a breaker bar.