Here's a link to BLM maps of Vinegar Creek to Hammer Creek:
Boater Guide - Vinegar Creek to Hammer Creek
I think there was one day on our Main/Lower trip last summer where we went a ways in the Middle section before finding a good camp, but generally we did not have a problem finding decent camps.
There are some rapids between the Main and Lower where you need to be awake.
Also, Whittis and Vinson put out a new river guide (their guides are my favorite river maps) last year that includes Hell's Canyon and the Lower Salmon. I think I missed it initially because the Lower Salmon is in the second part of the title and my internet searches for Lower Salmon guides did not find it. I just happened to see it in one of the rafting company offices when we stopped in Riggins.