I purchased Dax's rear 3/4 gallon fuel tank and rear rack a few months ago:
http://thatsdax.com/ENGINE_KIT_PARTS_PAGE_2.html
When it arrived, I didn't like the fact that the fuel petcock is located at the furthest end of the tank. It's sticks out like a sore thumb. The fuel line is vulnerable to being damaged by some opportunistic vandal.
Disappointedly, I let the tank sit. I almost sent it back to Dax.
After mulling over it for a long time, I had an idea.
I reversed the tank in its mounting rack/carrier.
The petcock and gas cap are now towards the front, right behind the seat. This tank's original mounting brackets are not perfectly matched to this fuel tank. I simply tweaked them a bit to reverse-mount the tank.
Now the petcock is 12" closer to the engine, 1/2" above the right seat stay. It's in a much better, protected position.
The rack's cross-brace was now situated directly above the gas cap, so I hacksawed it off.
I also installed a locking gas cap similar to this:
http://www.partsforscooters.com/134-15-Gas-Cap?sc=31&category=133063
The tank's lip just had to be filed a few millimeters for the cap to fit perfectly.
I like the Dax tank MUCH better now, since I reversed it in its mounting rack/carrier.