While researching the weatherpack stuff I found this site..
http://www.whiteproducts.com/faqs.shtml
It has some pix of the connection and has a link to instruction on using their crimper.
So based on this page, yes..... you do place the rubber seal into the crimp. With their instructions, they also place the terminal into the crimper first and then feed the wire into it.
http://www.whiteproducts.com/pdfs/T-...20w-photos.pdf