(Looking a little sleepy there Vance...

)
Even without chapters, you could still use the summary idea. I would suggest that at the end of each day's writing, you spend a few minutes writing a brief summary of what you have covered in that session (very brief: A meets B, argument, C intervenes, etc).
It might be best if you put this in a separate file so that you're not tempted to read over the manuscript itself. Then when you come back to it a few days later, you can read your summaries to that point and see where you got to, and then head to the end of your manuscript to start writing.