You'll probably have better luck with this question over in the Touring forum, but my thought is that if you're just looking to do this one, short trip and may or may not do more loaded touring in the future, get the bike you want for the 99% of your riding, and adapt it as best you can for this trip. I think a carbon frame would be fine for fitting with an axle mount trailer for the one trip. Rather than a BOB, though, I'd look at an Extrawheel trailer (http://www.extrawheel.com), and just pack your stuff in panniers to hang on it.