Your trailer should have been equipped from the factory with a black tank. It was mounted above the floor under the toilet. Check the photos on Vintageairstream.com archives. Since you have no tanks, some previous owner must have had a vision of some sort and made changes. Be sure to check ALL the plumbing for other changes. I'm in the middle of installing black and grey tanks to a '66
Caravel which had also suffered "previous owner syndrome" and I can tell you that the previously posted estimate for custom-made tanks is LOW. In addition, you will need all drain piping, slide valves, etc. Your Safari has more ground clearance than the
Caravel, but you still have to be concerned, especially if you are going to mount the tanks below floor level. Remember, "everything" flows downhill. Darol