I do not have the Viar tank, but one of comparable size (I think). Initially I did not like the way the tank sat under the Jeep, so I moved the locker pumps inside the cab. This allowed me to move the front part of the tank above the skid. The tank is out of sight and out of mind. Somehow I have managed to avoid pulling off the cheap drain you can see in the picture:
I do think the tailgate idea is an interesting one. If you do not need the storage space in the back hanging the tank off the tailgate would be pretty slick. They are generally light weight and would provide you with a good drain route. I speculate that if you burned a long piece of flat stock along the top edge of the tailgate (end to end) you would have enough material strength to hang the tank. Maybe you could integrate it into the hinge and latch mechanisms.

I do think the tailgate idea is an interesting one. If you do not need the storage space in the back hanging the tank off the tailgate would be pretty slick. They are generally light weight and would provide you with a good drain route. I speculate that if you burned a long piece of flat stock along the top edge of the tailgate (end to end) you would have enough material strength to hang the tank. Maybe you could integrate it into the hinge and latch mechanisms.