pics are small; the red tank? Few thoughts:

- Heat. The sun will heat that thing up real quick, and fuel may expand and spill out.
- Tracks. Many tracks (e.g., VIR) don't allow you to bring in outside fuel. Hard to enforce, unless it's in a big red tank on an open trailer with the words "HEY! I HAVE FUEL IN HERE!!!" on it...
- Safety. External tank is subject to road debris.

Putting some kind of cover over it will help all three.

GA