Gas smell when airco on?

Normal? Definitely not.

Common? Very.

As far as the gas smell goes, you almost surely have a gas leak somewhere in the engine compartment. You need to go ahead and take care of it, as if it is neglected you can end up with a fire.

For the exhaust smell, you may have a hole somewhere in your exhaust system, or in your air intake.

If you are mechanically inclined, below is a link to a tech article on how to find fuel leaks.... Otherwise, ask people for recommendations for a good local independent mechanic shop. Most dealers DO NOT have any special expertise with Zs, and typcially will be more expensive.

http://www.twinturbo.net/ttnettech/fuelleaks/fuelleaks.html

Good luck,
Matt