I use the scrolling text box just for that long document. The scrolling within the fixed Window looks good and I don’t lose navigation, which people always complain about. Personally I hate when my navigation disappears so that I have to scroll back up to find it.
Thanks for your help though.
@Radjin, You can fix your navigation to the top of the page so it stays in place like how I have done here - https://pcbeng.com.au
What you see in the example is I selected the background widebox, the logo, and the links, and then grouped them. Once grouped Sparkle will give you the option in how the group behaves in the right-hand panel. Tick the “Stick to page top” and you will be one happy person! 
That helps a lot. Even if I lose the footer it keeps the navigation and title. I will try that out tomorrow when I have time.
Thank you.