Hi bro
The website auto-saves your posts.
So even if you stop half way through, you can come back to it hours or days later and finish it.
Just click on "start new thread" again, and then click on "restore auto-saved content" and your post will reappear and you can finish it.
Or you can write it up in Word or Notepad or whatever and then cut and paste it into the forum website.
That's what I often do.
You don't have to have the forum website open and all you have open is a Word document.
I often write up Reports at work this way. No one has any idea what I am up to.