BFD2 works perfectly fine on a laptop, as long as you configure the machine correctly. The great thing about BFD2 is that the engine can be configured in multiple ways. Depending on your machine, you can adjust most of the settings in BFD2 to optimise performance based on your computer and playing style. I do not have any problems with this setup in a live situation.
This last year I have been using a MacBook Pro with 4GB of RAM. No problems! In Fact, we use laptops at tradeshows and run them constantly for eight hour stretches. You could also get the same results on a PC platform. Yes, you need a second drive for the samples. I just got a 320GB Portagig drive from Glyph. It is 7200 rpm and just a little bigger than a pack of cigarettes. A Laptop, interface, and a small drive is not that much to carry around. I have my entire rig in a two space SKB Studio Flyer luggage style rack that fits in the overhead bin on a plane.
The bottom line is not to try and cut corners with the laptop, or any other machine for that matter. Buy the fastest, bestest, most complete computer that you can. In the long run, short cuts will cost you more money than if you buy correctly the first time. My MacBook Pro is two years old, working great, and I expect to be able to get a couple of more years out of it!
I recommend asking questions about configuration advice at www.FXpansion.com/forum
Hope this helps,