I do have to re-sign in when I come here via laptop but not on my desktop, don't know the reason but do find it rather aggravating.
I don't lose the post when I have so sign in again though.
Notepad is definitely an option, so is copying your text every few minutes and then pasting it into the form after you sign in again.
I think the time out feature is set to 10 or 15 minutes if the program doesn't detect you being 'active' by clicking on other threads. Just typing or scrolling to read doesn't count as active, unfortunately.