There is a huge misconception about .jpg degradation associated with saving them repeatedly... it depends solely on what you actually do to the .jpg that determines if you will lose pixels when saving. For most users, the slight degradation you get with multiple saves is so minimal it really is an over-hyped issue.

However, it really is safer to just use .tiff, .psp or .psd files in any event. It is simple to convert them to .jpg when you need to use them for outside printing or web publishing.. and then you can delete the .jpg. Your master becomes the layered file and you generate temp copies as needed from them.