I'm sorry you had the problem of being logged out too soon.
When you sign into Psych Central there is a tick box next to where you put your username that says "Remember Me". If you tick the box at sign in, you will not be logged out (unless there is an issue with your ISP).
Many times, when I am going to write a long post, I write the post in notepad on my computer then copy and paste it. I keep the thread up so that all I have to do is click on the tab where the thread is and viola.....done!
I hope you find this helpful.