In TN we have a stupid law that rifles cannot be kept in a vehicle while loaded. Loaded is not defined in that statute but in others it alternatively means chambered (condition 1), not chambered but loaded mag inserted or unchambered with no loaded mag inserted (condition 4). To be completely safe, I would need to vehicle carry in CONDITION 4. Not happening.
This means when the law is dumb, avoid it. That means taking one of my stripped lowers and building a 14.5" barrelled pistol with a Gear Head Works Mod 2 brace and using it in place of the 18" barreled rifle I want to have in there.
Qualifications
must be in stock or commonly so
must not be expensive -- see truck gun built only to meet stupid law
must not be a generic from Bob's basement AR builder and meth lab -- no Century products for sure.

5.56 - preferably 223 wylde but certainly not mandatory.
not a clamshell - Pic rails, M-Lok... whatever is fine
I realize I can build one, but I would prefer not to although if no decent options at a decent price exist, I just might have to.