Cannot install bootcamp because of disk error, but disk utility says it's fine?
You are probably asking the wrong question. If I were you, I would be asking about the 296.6 GB of free space which appears in your Logical Volume group. If you can get most of this free space added to you Logical Volume, the bootcamp install would probably work.

According to the accepted answer to How do I recover free space from my logical volume group?, you would probably be better off recreating the Fusion Drive, instead of attempting a repair.