You would be surprised. I've seen some pretty talented work done on ATV plastic in the past. Almost as if the erase a full layer off the top and come out with a like new piece. Hard to find someone that will do little specialty jobs like this though.
You're going to have to roughen up the interior of the tank though, to help the coating adhere or stick to it better. This is good stuff though, no pealing off, or flaking.
There is a guy on here that gave me some pointers on this stuff...can't remember who it was off the top of my head. Pretty sure he had a beard, and is somewhat of a celebrity in the west coast mini bike world...
Good luck buddy, and share your "how I did it's" on here. In the future more people will be using this stuff.
cd