If it is woven acrylic, use any fabric waterproofing intended for synthetics (not canvas). SOme brands are Camp Dry, Scotchguard Outdoors, 303 Fabric Guard, etc. If its vinyl, it can only leak through a hole, which includes where the stictching goes through it. Apply waterproofing to the stitches.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL