People talk about having a 'truck gun' but I want to take that idea a step farther and do a 3 gun system. I am day dreaming--so it's for fun [so far], but it also does have a manner of seriousness to it because I might make it happen at some point, or at least get the weapons

I have a couple of different iterations or ideas but I would like to hear your thoughts about the subject, this is particularly and specifically if you were able to customize the interior to some degree of the vehicle to be able to secure the weapons when you aren't in it.

Idea 1

Either go 9mm or .45 ACP in a full size Glock. At the same time do a shorty short PCC SBR or 'pistol' with a brace on it and a 3 lug mount (and of course a 3 lug equipped can). Then you can just load the holy crap out of mags (all compatible) with 147 grain hollow points [or .45] and there will be no compatibility questions. An additional gun would be a 00 buckshot shotgun. Not sure if a pump or a semi auto or what variety would be best. I lean towards semi auto and maybe even something magazine fed but I am not sure and would like opinions.

The pistol in this case would be secured inside the vehicle and not meant for on your body carry so something full size.

Idea 2

An AR of some variety and caliber (input requested) with a pinned and welded suppressor to make it only a one stamp gun. Which caliber would you go with and why?
Same question(s) as above about the shotgun.
The pistol could be any variety that I like (I love my P226 but I am open to other ideas). Again though, this is not intended as a replacement of the on your body weapon.

The idea is to be able to secure the weapons when you are not in the car so consider that part as 'already accomplished' for the purpose of this discussion. Which weapons would you choose and why? And of course who doesn't need a mini gun, but I am talking more about a realistic system for outfitting a vehicle.