For car seat concerns.
First, you have at least a potential weapon that weights a ton or more. Many forget that you can speed off or use your vehicle to power your way from harms reach.
Second, vehicle carry only applies with a CPL (concealed pistol license). See OC rules
Third, when OC in vehicle with CPL - be careful as you don't want to have someone say you flashed your firearm on them. When pulled over you'll have almost no argument with the police.
So, is it comfortable when seated? For self defense it's get away from harms way. If you are looking at some terrorist wanting to kidnap you (get your car armored up).
Back to reality:
If you have a CPL you can have it anywhere within reach of you. If your passenger has more "access" to it then you and they don't have a CPL (e.g. glove compartment)... not a good idea. There are several threads here on how folks have mounted their sidearms within reach of them. Again, if you don't have a CPL and you get pulled over - your busted. You'll need to unload your firearm before you get in the vehicle (for OC carry without a CPL).
Lastly, the more you handle your firearm in public... the more likely someone can call and say your were flashing the firearm at them. Once holstered don't mess around with your firearm in public areas.
Everyone has cameras so you just never know who is taking pictures of you.