Bowen Water heaters are Atwoods or Atwoods are Bowen... They are now branded Atwood but are the same). For comparison, look at the plain LP (or electric if you have electric) Atwood diagrams. The drain for the Bowen/Atwoods are on the face. BTW, you have a very old water heater. From what I can tell, it looks like the cold water inlet (hot water outlet should be higher up) Check out page 26 of the PDF (link located below)
Atwood Water heater Service Manual
YOU NEED THIS!!!!! DOWNLOAD AND SAVE!. This is the Service tech manual for the folks who work on the units. Except for the fact that our current Atwood water heater (replacement) is newer, it is pretty much identical to the vintage Bowen that we suspect was original to our RV. It developed a small leak in the tank. So it got replaced.