The further that tank is from the ground the better.
You don't want your gas tank 3" from the ground, and It would look just silly.
anyone behind you would see the thing.

Also...would make it MUCH easier to steal the gas out of.

And, how often do you remove the gas tank?
The one in my truck hasn't been moved in 60 years.

If its ease of access you are after, place it in the bed. Safer, and easier to get to!