I did my 12 year old (at the time) Sunbrella Tonneau cover two years ago. Washed it in a
heavy duty washing machine in a Laundromat. We used "Woolite". We air dried the cover over a picnic table.
Once the cover was dry..we used
"Waterproofing..with Teflon" from West Marine..in a Spritze bottle. It has worked well. The area of the Tonneau Cover was maybe 7' by 10'. We used almost all the spritze bottle. It will look like the fabric is
saturated when you are done. Then it drys in an hour or two.
NB