Just last night I saw several sellers of doors on ebay - go to vintage parts and type in keywords "rat rod" - then scroll thru...
Yes you need more than the door skins - you need a frame, hinges, handles - some of the original ones even used wood as part of the frame... It will be a lot of work and money to make it so doors will open (you would even have to make door jams on the body for the hinges and locking mechanism to bolt to) - cheaper and easier to make a it into a tub... You can incorporate door skins to give the illusion of doors... If you do make it a tub, channel the body over the frame so it will be easier to step into, you might want to consider this when you order your frame - Z it so the body section is lower...