Kayak Seat Pads: The cheapest was the best for me.

[alanw]

I have been trying the Thermarest one you linked from Sports Chalet. Mine holds air all day, no leakage at all. It's pretty comfortable once you get used to being an inch higher than normal and the extra movement you get from sitting on it. It also has to be strapped onto your existing seat if you want to make sure it doesn't slide around. So far it's better than any foam pad I've tried.