I think the introduction of cars as they are in fallout tactics without tweaks would hugely unbalance PvP, since the big factions would be the first to have the heaviest/most armored veicles (who else has that kind of money?), fill them up with their best PKs and go on a 'killing spree drive by' in Modoc, but on the other hand I really like that idea, so let's try to make it work...
Problems:
One Hummer (for example) can transport 8 players, 7 of which can shoot out of the car while it is moving around town. As a bystander you don't know how many characters are in there, what weapons/armors are they using, you can't target shoot them in eyes/arms to hinder their ability to keep shooting at you, you can't attack them with melee attacks and the car can even invest you if you're not fast enough to get out of its way.
If you are in a gang fight PvP and an APC comes in you have to completely destroy the veicle before even seeing who are you being attacked by and start causing them any kind of damage and by then your side already lost half of it's fighters...
There must be penalities and/or greater risks when using veicles in combat to balance out these tactical advantages ...
Suggestions:
1. When a car is disabled (0 hp) while moving it stops and all people inside are all thrown out of it in the direction the car was going (as if they were knocked around by explosions) with a little damage. If it was standing still they just all disembark. Additionally cars should suffer from critical hits as creatures and catch fire or explode if disabled by criticals (causing even more damage to the people inside).
2. Cars can be repaired only when inactive (no driver inside), to avoid smart asses using mechanics inside the veicle to repair it while it's trolling around town wrecking havok...
3. You should need either a profession to learn to drive a car (brahmin caravans are for all without profession, maybe lvl 1 for buggy, hywayman and scout; lvl 2 for hummer and apc, lvl 3 for verbird/tank*) with Pe and In, repair and science or outdoor skills requirements, or alternatively switch gambling or speech skills for new driving skill as in fallout tactics.
4. Cars obviously should have a decent damage resistance and damage treshold, 0 armor class when steady, 10 Ac when moving, but also they should reduce the field of vision of the people in them (-1 Pe when steady, -2 Pe when moving) and give a penalty on ranged attacks made while the car is moving (you could also introduce some of Fallout tactics perks related to cars like, gunner and road warrior to mitigate these penalties).
5. Once you buy/craft a car you must choose a 'name' for it (whats written on the registration plates or painted on the hood (bonnet)) and that name should be visible on the top of the car (so basically treat a car like a 'construct critter' with it's own name) so people can kind of recognize different cars even if they don't know who's inside. Once examined by a player, the description of the car should say how many characters appear to be inside the car and how damaged it is. If you have Awareness perk you also see the Hp, Ac and upgrades on the car, but still can't identify it's passengers.
6. Maybe introduce in FO land mines (just add them to demo expert profession) to give factions without cars a chance to crate obstacles/mine fields on the main street of a town they are trying to take over, to counter incoming big faction apcs marching in killing everybody without a fighting chance.
7.* Make cars craftable/upgredable with new high requirement mechanic profession (In 8-9-10, science 80-120-180%, repair 110-150-190%) and insane ammount of resources. Cars could be crafted only in garages (like the one in new reno) and maybe the top level base (360k?). Fuel should also be entirely craftable.
Lvl 1 makes: brahmin caravan (2 tamed brahmins, 100 junk, 20 tubes, 30 metal parts, 12 alloys, 300 wood, 12 hours cooldown), and Buggy (250 junk, 50 tubes, 60 metal parts, 30 alloys, 50 wood, 15 brahmin hides, 20 fibers, 18 hours cooldown).
Lvl 2 makes: Scout (400 junk, 35 tubes, 120 metal parts, 60 alloys, 30 wood, 5 brahmin hides, 10 fibers, 24 hours cooldown), and Highwayman (600 junk, 30 tubes, 150 metal parts, 100 alloys, 40 wood, 20 brahmin hides, 20 fibers, 48 hours cooldown).
Lvl 3 makes: Hummer (1000 junk, 100 tubes, 500 metal parts, 200 alloys, 50 wood, 25 brahmin hides, 40 fibers, 72 hours cooldown), and Apc (1200 junk, 200 tubes, 1000 metal parts, 400 alloys, 100 wood, 40 brahmin hides, 50 fibers, 96 hours cooldown).
Note these are just sample figures I made up in 10 minutes, they have to be adjusted if it turns out to be too low/high...
Once bought or crafted cars could be upgraded and tweaked by professional mechanic of appropriate level; some upgrades could be Extra armor plates (extra dmg resistance but speed penalty), armored windows (extra armor class but Pe penalty for those inside), extra fuel tank (greater fuel capacity but also grater chance for the car to suffer critical hits), turbo charger (speed buff, but greater fuel consumption), mine sweeper (car suffers less damage from mines but has a speed penalty) ecc...
This whole point is to offer an alternative way to get/personalize cars, beside buying them for great ammounts of caps and also to give lvl 21 people something to do (I'm sure soon there would be player run car markets:)
So, these are my thoughts on the matter; I'd really like o see cars and some more professions in FO as it would give more RP options and add interesting tactical choices to Pvp.