The program does support encrypting USB and portable hard drives and the software is included on the drive, so you don't need to have it installed on the machine you are using.
The portable version already exists and is available within the GOTD version.
Read about the "USB Flash Drive Vault"
http://www.sensiguard.com/faq#install
"The USB feature is free and never expires. It is added to your computer when you install SensiGuard. Even if you don't purchase the full version of SensiGuard after your trial expires, you can continue to create USB vaults forever on an unlimited number of USB drives and safely transport files to/from work, school or home without the need to have SensiGuard on any other computers."