I get a couple 2x4s studs from home depot get them to lop about 18" off and put them across box rails, then put the new box inverted on top with a couple straps to hold it in place. Has worked for me with transporting boxes for a couple/three hour drives.
I can't help with the NY rust; but with shape your box is in, I would be tempted to just grind the heads off to lift the old box off, then replace with new. I had to do that with the ones where previous owner had installed a body lift - bolts were seized into the lift blocks and weren't coming out...
I can't help with the NY rust; but with shape your box is in, I would be tempted to just grind the heads off to lift the old box off, then replace with new. I had to do that with the ones where previous owner had installed a body lift - bolts were seized into the lift blocks and weren't coming out...