Ok, all things considered, shooting out of cars that block the driver is totally possible. It's been possible since Seat Weaponiser 1. I have a very simple work around that would let you shoot out of these types of cars.
There's a good reason I haven't added it in though, and that reason is that there's no good optimized implementation that would work for everyone. I'd also like to remind all of you that being able to use this in any vehicle is a beneficial side effect, as this addon has always been about being able to shoot from custom-built vehicles and seats, not workshop cars.

The method is basically this: I draw a line starting from the outside and ending where your face in the vehicle is, and wherever that line hits on the car body, I edit your bullets so that they come out of there instead of your shoot pos.
This is a very simple work around for vehicles like the default Jeep and Airboat, and would even work for something like TDM Cars, if you're the driver. But that's where it gets more complicated.

Popular vehicles addons like to have passenger seats, and these passenger seats are their own separate vehicles that are spawned inside the main vehicle. I think TDM Cars and Slig Wolf's various vehicles do this, and I know for a fact that SCars and WAC do this, even for the driver.
So the problem now is that the "car body" is only the seat you're sitting in, and not the car as a whole.

Does this make it impossible then? Of course not, there's a workaround for this too. I can "scan" for all the stuff that's connected to the seat you're in, and count that as part of the car. That way you can still shoot out of close-hood cars.

But now we run into a whole host of other issues.
People will now be able to make miniaturized bunkers or pillboxes, set them to transparent, then weld them to a seat. When they sit in the chair and start shooting, they are effectively invincible to most forms of weapons, but my code will let them shoot out of the bunker. This is bad for obvious reasons.

On top of that, people could maliciously abuse this code in another way: Make a contraption that has hundreds of props, weld them to their seat, and then start firing full auto with the fastest gun they can find. Since I have to scan every single prop that's connected to the seat when I draw the line, this would potentially lag and maybe even crash servers, especially weaker ones.

THE BOTTOM LINE IS:
I can't make something that will let you shoot out of SCars and whatever other vehicles you're using that have closed hoods. The problems outweigh the benefits.
HOWEVER, I can make it so you can only shoot out of jeeps, airboats, and the drivers seats of TDM cars. This would also allow people to use the Prisoner Pod as a weaponiser compatible seat.
Expect an update sometime.