Avoiding static shocks from vehicles
In most cars, you are isolated from the chassis when you're driving: everything is plastic, leather or textile. When you get out of your car, friction can rip off charges from the electrically neutral environment (this is called tribocharging) such that the potential difference between you and the ground increases drastically. When you set foot on the ground, your shoes are normally isolating you sufficiently for you to retain that charge. 

On the other hand, the chassis is pretty much at ground potential: yes, it is isolated from ground by the tyres, but there is still electrical leakage through the tyres so over time, any difference of potential leaks out. Therefore, when you touch the door to close it, you are effectively triggering an uncontrolled discharge to ground. As you guessed, the so-called antistatic strips will not help you because the chassis is already pretty much at ground potential.

This is the same thing as the protection against electrostatic discharges in chips. Standard practice is to never use isolating materials (which prevent equipotentiality) nor conductive materials (which do not control discharges) for your environment, but dissipative materials instead. Now, you are not going to redo the interior of your car with dissipative mats, but you can still control the discharge the way you prefer.

Personally I would place a small metal plate in the door near the handle connected to the chassis via a 100k-1MOhm resistor (which makes it a dissipative material), or even hack the inside handle to make it nicer. Touch it after you are finished rubbing yourself against the seat and before you close the door and you should be fine.