Any waterproofing suitable for synthetic materials (not canvas or leather) will work fine. Starbrite makes a product and one is offered under the West Marine logo too. Outdoor recreation outfitters usually have something too, for nylon tents and flys.
If yours is leaking that quickly, something has taken off the factory applied waterproofing, which usually lasts many, many years. Heavy scrubbing can do that, as can strong bleach treatments and petroleum-based solvents. Or maybe you just camped in an area with a particularly nasty acid rain.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC