I have the Advantage Hard Hat tri-fold tonneau cover, which is essentially the same as the GM-branded one but a lot less expensive. The only difference is that there is no GM logo on it. http://www.advantagetruckaccessories.com/hard-hat.html
I have had it for about 2 years and it has held up great. Like the OP, I wanted something that would sit on top of the frame rails, was easy to put on/take off myself, did not require any brackets, frames, drainage tubing, etc., and was relatively water tight. This thing fits the bill. IMO it looks great, its easy to use, durable, and I can take the entire thing off/put it back on in about 2 minutes.