So after spending 6 in-game days sitting inside the starting evac shelter, cheating my way to a modestly large custom 5x6 vehicle, and wanting it to be as durable as possible, i've come to the conclusion that large vehicles just arn't worth the time and materials ... to fully armor. Why? Literally chewing through 3 1/2 fully charged welders to create the vehicle, but then 3 more welders to armor plate everything. The mass of the vehicle basically doubled, and the K-x%'s dropped like crazy.
If you have to armor a vehicle:
1. Prioritize armor to areas that will be hit by impacts the most. Usually, this is the front and all external wheels. Internal areas that don't have components shouldn't need armor, or should be armored last.
2. Glass windows do not seem to be safe against impacts. Building an impact zone in front of your windows out of frames and armor plates, instead of plating the tile with the window directly. These frames will get hit first, and the glass will last longer.
3. Go under 30 while on a bridge even with considerable driving skill. Hitting zombies can cause control loss, and vehicles are deleted entirely when their base tile (the tile you started the vehicle construction on) hits the deep water tiles that surround bridges. I learned this the hard way for the second time after my cheat-vehicle above fell victim to this.