I doubt the vinyl offers much in the way of insulation. And for what it's worth I'd take Sunbrella over vinyl any day of the week, twice on Sundays. In marine applications a well cared for Sunbrella canvas can last a very long time. I know this first hand.
Buy the 3M Sunbrella spray. There is a specific type endorsed by Sunbrella in the 303 line. Clean the canvas, spray twice per year and enjoy an outstanding fabric. Far better than vinyl in my humble opinion.
If you don't want Sunbrella I'll trade you my one year old vinyl A8 cover, straight up.