I installed BT4 final on my USB in the persistent mode working according to the tutorials (mainly the video, at offensive-security). my USB is 8gb and i parted 1.5gb for the bt4, and another 0.5gb for the casper-rw file (for persistence).
of course 512MB is generally not enough for it. but i need the other 6gb for file storage.

However, the casper-rw is getting full pretty fast, and even small changes such as using FF3.5, or changing few gui options seem to take lot of space. (not sure that is the reason, but it certainly getting filled up fast, and besides those thing, I haven't done much).

As well, I would like to update packages, but doing so would fill up my casper partition in an instant, and following the tutorials that are mentioned about modifying a live CD, would mean that I would need to update and install the new live CD again to the USB, or, in case I would give up on USB-edition, to burn it to a new DVD every time I update.

So, the main question is: Is there a way to install the BT4 completely to a usb ? I assume it's like installing to a hard disk, but how much space do I need? and is there anything else I need to think about or change in order to make this work?

Also, if there are other options or ideas that can help me with the situation, I'm open to suggestions.

Sorry for the bad english :\ and for being an not-really-knowing-over-the-head noob