

PORTABLE HARD DRIVE FOR MAC AND WINDOWS INSTALL

Uncheck "Create a Windows 7 or later version install disk".
PORTABLE HARD DRIVE FOR MAC AND WINDOWS DRIVERS
Erase the disk using diskutil eraseDisk fat32 DRIVERS MBR /dev/disk2.In my case, the device name was /dev/disk2. Run diskutil list to determine the device name.

Download the Windows 7 Automated Installation Kit from.VMware Fusion 7.1.3 couldn’t connect my external USB disk to my Windows VM.The non-professional free evaluation version is sufficient.Install VMware Fusion 8.1.1 from VMware's site.Driver drive: SanDisk Extreme 32GB USB 3.0 Flash Drive (SDCZ80-032G-GAM46).Destination drive: Samsung T3 Portable 500GB USB 3.0 External SSD (MU-PT500B/AM).In addition to the external drive that will host your Windows installation (the "destination drive"), you will need another USB drive (the "driver drive") to temporarily store the Boot Camp drivers. I found that certain operations failed more frequently if I used the USB hub in my monitor. Throughout the process, directly connect all devices to your Mac. I tested this process on a MacBookPro11,1 running OS X 10.11.5 (15F34). Here's an updated procedure for Windows 10, based on orkoden's excellent answer.
