Well Ive had a good look and I'd have to say I haven't found quite what I want among encryption or folder lock type programs.
I need something that resides on my external drive and is independent of the computer I attach it too. Most of the solutions require admin access to the target computer or want to load or leave a driver on the computer and won't work if they can't or leave the decrypted file visible unless I remember to delete it. I found "folderhideking" which is a so called green installation but it is a very fragile looking piece of software at this stage.
I'm not on Linux BTW.
Folderhideking seems functional enough but I am hesitant to pay $US20 for it as it seems very clunky. This is probably because of a language issue since it is of Chinese origin. Eg in the help menu there is a link to older (sic) the program. Clicking on it leads one to a Chinese language site. However if one goes through Simtel one has the choice of Share-it and Qwerks to place the order.
However I think I've found the answer ... StompSoft's Portable Vault. I installed, ie copied to the root directory of every flash drive/USB external disk I could lay my hands on and it worked like a charm. No "you need admin privileges", "I can't load the driver" or "Service can't be started messages". Members should be aware though that the trial version is very limited with respect to the size of files which can be encrypted and the full product supports only one encryption algorithm. But it works beautifully smoothly and is only $US15.
I haven't bought it yet as I'm considering it's older brother Digital Vault. I have sent a support request to StompSoft about wether it will work OK on portable drives.
I hope this is of some help to members at some time.