Zip file password protection is realy insecure, given the speed of modern machines and the weakness of the method (just google zipcrack).
It also seems silly to wrap a .tar in a .zip. In the unix tradition of using programs which do one thing well, I'd be looking for a stand alone encryption tool. gpg will do the job if you want to use it. There are others, although I cannot vouch for their strength. Searching the ubuntu repos finds bcrypt and ccrypt.