I think players driving have a huge disadvantage when they are solo. Maybe you could consider making a distinction between 2 handed weapons and single handed weapons. This way a player driving a boat, a car, a mini can shoot single handed weapons.
1) players must ADS in order to shoot while driving
2) accuracy reduced by 30%
3) unable to turn the vehicle left or right when shooting (just accelerating)
4) Custom SMG should be able to be shot single handedly too (new difference to make it more appealable over the superior thompson) with the standing recoil pattern
5) other usable guns while driving: all pistols, nailgun, consider crossbow
6) increase reload time when driving