The howto referenced above is also hosted at;http://www.mumble.to/linux/d900t-install.html
In addition to the recommendation for following the Gentoo docs for your install, I would suggest that there's little bits and pieces in the howto that seem dated. The reference to SATA driver support at the beginning and the patch for baselayout at the end in particular. The big challenges will be to pick the right SATA driver for your controller, and then to configure things like your WiFi and other hardware components correctly, (the howto seems like it has good information in these regards).
In addition to the Gentoo docs, the BEST place for questions with specific hardware issues and Gentoo, are at their forums. I've learned a ton there myself.. I searched there for Clevo D900T before coming here and the following was posted, which may help you (again some of it may be dated);http://forums.gentoo.org/viewtopic-t...evo+d900t.htmlhttp://forums.gentoo.org/viewtopic-t...evo+d900t.htmlhttp://forums.gentoo.org/viewtopic-t...evo+d900t.html
Lastly my Toshiba laptops support RAID configurations as well, but I would never use it on a laptop. Especially in a RAID 0 config as the howto author has indicated. You only need one problem with one drive to kill your entire volume. But since your laptop supports it, you may want to try it.. If you do, be careful and backup often..