Road War rules question

So we've got the Murder Bus loaded with the hardholder's gang (the Scorched) being chased down a ravine by the War Pigs. The War Pigs crew are riding an unarmored dune buggy and a heavily armored sedan.

He wants to use his gang as a weapon to seize by force the vehicles. Do you allow this move without having them board a vehicle first? And if so, do you stack vehicle armor with the armor of the occupants?

I am thinking of allowing it without boarding first but having vehicle armor and occupant armor stack. And saying that if you do manage to board the vehicle first, you can ignore the vehicle's armor.

Only reason I can see to not allow the move in a road war is because someone with low cool is never really going to use the road war moves; they are always going to try to use their guns or gangs in a road war.

How do you all play it?

And just to be clear, he is not trying to take posession of the vehicle with the seize by force move. He is trying to take it off the battlefield by rendering its driver incapable of driving.

Personally, your Hardholder has two weapons here (plus any gear he's carrying), a gang and a bus. Either one can use the battle moves. Check the refbook pdf, harm rules pg 2.
When you’re behind the wheel, you can sucker someone, go aggro on them, or make a battle move, using your vehicle as a weapon. By extension, you can make those moves using a different weapon.

Now it sounds like what he really wants to do is Single Combat, not so much Seize By Force. If he wants to use the vehicle to inflict harm, they'll be using theirs to inflict harm back. If he wants to use his gang, the people inside the opposing vehicle will inflict harm back. The damage that's inflicted goes to When A Vehicle Suffers Harm (same page), which includes how much of the harm a vehicle takes will punch through to the people inside of it. Note this for the unarmored buggy:
Whether harm blows through to a vehicle’s driver and passengers, doesn’t blow through, or just hits them too without having to blow through, depends on the MC’s judgment of the circumstances and the vehicle.

That's the straight forward part. Now the interpretation part. It makes sense (seems real) to me that a large gang with shotguns can do more damage to a vehicle than one guy with a shotgun. It might make less sense that a small gang in a vehicle causes it to take less damage than just having one driver but since this isn't necessarily a blow-by-blow, combat rounds type thing, I'd probably go with it. So if there's more than a couple of guys in either vehicle, that's a small gang and modifies the damage based on the size of The Scorched.

Now if he wants to board instead, I wouldn't have that automatically ignore armor with the sedan. Think of Mad Max or Indiana Jones jumping onto a moving vehicle. They land on the roof or the truck bed or whatever and have to work to get inside. If they want to shoot through the window or something to ignore the vehicle, that's probably going to be Acting Under Fire to avoid getting thrown off. If an NPC pokes their head out to shoot the PC/his gang, they're a valid target. For the buggy, there's not much outside to be on. Once you're on, you can start shooting.

I'd play it with seize by force, no additional moves or complications required. The rules for vehicles' armor and harm blow-through should work just fine with the rules for gang vs gang harm.

I'd save boarding a moving vehicle for times when the PC wants to do exactly that.

Definitely don't use single combat for this!

-Vincent