This is actually pretty dang good.
Some tips for others: (because that's the only reason why anyone besides the author reads reviews)
1. Like Xenogeist said, you won't get all 20 trucks through. Don't worry about it.
2. Burst fire weapons! I used the assault rifle as soon as I could, and it works like a long range shot gun. The best out of all I tried.
3. Get the car upgrades first, then the middle two (for the balloons) and then combat for the ammo.
4. I found that large tires in front and back prevented stuff from jamming between my wheels.
5. Also like Xenogeist said, use the 3 spike tires on the blockades, about a second before you hit them.
To the Author:
Excellent work! It required strategy, skill, and luck which is more than a lot of games. I also liked how you could see your fallen drivers and zombies! Very nice touch.