I thought there is a more professional way of doing it.
If you want to store your "Encrypted Wallet" permanently on a USB you can install the whole of Bitcoin core to the USB, then follow the instructions in the quote to make it use the wallet.dat on your USB.
Click the "shortcut" tab in the properties window, then look for the first text box in it labelled "target". Copy the line of text below and paste it to the end of whatever is in the "target" text box.
-datadir=.
Make sure you copy the leading space and trailing . from the line of text above.
The text box should look something like this.
Afterwards click the "apply" button, then the "OK" button to close the shortcut properties window.
Copy your encrypted wallet.dat file to the same folder on the USB that contains bitcoin-qt.exe.
Double click the new shortcut to run Bitcoin core. Don't double click bitcoin-qt.exe because that will make Bitcoin core look for a wallet.dat file on your computer rather than on the USB.
As achow101 says your USB wll need to be over 120 GB to run Bitcoin core from it.