I've thought about a seatpost clamp style rack but they look kinda flimsy
They tell you the weight limits, whether 15 pounds, 25 pounds, or whatever. There's quite a range of them.
--plus putting it on carbon fiber can damage it I've heard
which is why you would probably want to change the seat post to an aluminum one if you currently have a carbon-fiber one. It won't hurt the frame though. I've read of plenty of 250-350-pounders riding carbon-fiber bikes with no frame problems.
How good are seatpost-clamp-racks?
I have a Topeak RX Beamrack which, although I have never used it (I changed my plans after buying it), looks like an outstanding quality piece of work-- really nice equipment.
Also, how good is the Windsor bike? Why would you not want to go that whittierider?
The only company that distributes them has a terrible reputation for bad assembly, not coming through on customer service, false advertising, etc.. Some people have had good experiences with them, but there's a disproportionate number of customers who are extremely unhappy with them for these reasons. It does seem like they're trying to improve, and they got past their "Unsatisfactory" rating with the BBB which was a result of non-responsiveness to customer-service complaints, but it will be quite awhile before I feel comfortable recommending them.
If you had to carry a lot, the trailer mentioned above will work with your bike, but I'm sure you don't need that much for a tour of only two or three days. Depending on how much you need, you might get away with just a really large seat bag. They come in sizes up to nearly a cubic foot, kind of like a small duffel bag back there with internal braces to keep it from swinging and swaying. Here are a couple from Caradice, from wallbike.com :
You can add a handlebar bag too. If you're just credit-card touring (stay in a hotel, eat in restaurants), you might get away with a smaller seat bag like Jandd Mountaineering's Moutain Wedge III which has nearly two gallons' worth of space: