I do this quite a bit when I travel. How you do it is up to you, both have their advantages and disadvantages. You could keep a "Travel Catalog" on your laptop's hard drive and then import that into your "Master Catalog" on the RAID system. You also can just have your "Master Catalog" have multiple directories in it, some on your laptop hard drive and the majority on the RAID system. The catalog needs to live on your laptop though.
I have found that the more consistent system is to keep one single "Master Catalog" that has multiple directories in it. The reason I chose that approach is that I have found my keywording and labeling is much more consistent that way. Since I have one set of Keyword collections and one set of actions and preferences everything works the same.
The key for this style to be effective is to do all of the file management and moving in Lightroom, none in the operating system whether it is Mac or Windows. Doing it all within LR keeps the locations and database synchronized. Yes, it is possible to manually locate the files if you move items outside of LR; however it can be irksome.
What I do is have a directory on my laptop hard drive called "Lightroom Local Images" I know creative name. When on the road and disconnected from my external hard drive, I import all my images in to there in the Master Catalog. I do a year>month>day folder structure but have previously used it with other structures as well. In the Master Catalog you will notice that the folder for the external storage will be listed but all the images will be unavailable with question marks. That is normal. When you reconnect to the external storage it will attach correctly.
When you are ready to move your images from your local drive to the external storage, within the Lightroom Module you can simply drag the directory from location to location. You will typically get a pop-up window that indicates and confirms the move you are doing.
I can provide more information or an example once I get connected to my external hard drive if you have more question.