We sell and use lots of tents and waterproof gear.  When seams leak or the waterproof seam tape starts to peal, we like Seam Grip Seam Sealer.  The Seam Grip SIL is a sealant specifically designed for silicone treated fabrics, perfect for sealing silnylon tents, tarps and ultralight backpacks. A single 1.5 oz tube can seal up to 24 ft of seams, perfect for pinhole repairs and small tears, easy to use and weather-resistant. Keeps gear waterproof in extreme heat or cold.